Hm, nice Idea...
this script scans your download for any folders containing media data that iTunes can play,
and adds them to a corresponding playlist within iTunes
duplicates will be removed and playlist names no not contain _
just give it a try and see

Applescript:

-- hubionmac.com 10.10.2009
-- scans download folder for folders containing media data iTunes can play
-- creates a corresponding playlist within itunes
property special_bigChars : {"Ä", "Å", "Ç", "É", "Ñ", "Ö", "Ü", "À", "Ã", "Õ", "Ÿ", "Â", "Ê", "Á", "Ë", "È", "Í", "Î", "Ï", "Ì", "Ó", "Ô", "Ò", "Ú", "Û", "Ù"}
property special_smallChars : {"ä", "å", "ç", "é", "ñ", "ö", "ü", "à", "ã", "õ", "ÿ", "â", "ê", "á", "ë", "è", "í", "î", "ï", "ì", "ó", "ô", "ò", "ú", "û", "ù"}
property action_list02 : {"01-Abcd Efg", "02-Abcd efg", "03-ABCD EFG", "04-abcd efg"}

global folder2Scan, actionid


tell application "Finder"
   set actionid to (my get_selection_index(action_list02, "Format of Playlist_names (cancel for no changes)", false))
   
   set folder2Scan to folder "Downloads" of home
   
   set thefolders to every container of folder2Scan
   
   --get my download folder
   set thefolders_list to my makeDownloadPlaylist()
   
   --clean the folderlist from old playlist // option dialog would be nice
   my clean_iTunes_folder(thefolders_list)
   -- make a folder playlist called itunes or get reference to it    
   repeat with thefolder in thefolders
       set foldername to my do_string(actionid, my replace_chars((name of thefolder), "_", " "))
       --now the script loops through every folder, creates a corrensponding playlist
       -- if there created playlist is empty after all, it will be removed again =)
       tell application "iTunes"
           set current_playlist to my check_playlist(thefolders_list, foldername)
           add (thefolder as alias) to current_playlist
           if (count of every track of current_playlist) = 0 then
               delete current_playlist
           else
               --clean the playlist from duplicates
               my cleanPlaylist(current_playlist)
           end if
       end tell
   end repeat
   
end tell

display dialog "done...
***commerical***
created by hubionmac.com :-P
***commerical***"


on check_playlist(folderplaylist, playlistname2check)
   tell application "iTunes"
       set thelists to every user playlist of source 1 whose special kind is none and smart is false
       set fpl_lists to {}
       repeat with i in thelists
           try
               if parent of i = folderplaylist then
                   set fpl_lists to fpl_lists & {i}
               end if
           end try
       end repeat
       repeat with i in fpl_lists
           if (name of i) as text = playlistname2check then
               return i
           end if
       end repeat
       make new playlist with properties {name:playlistname2check} at folderplaylist
   end tell
end check_playlist

on makeDownloadPlaylist()
   tell application "iTunes"
       --    set thelists to name of every user playlist of source 1 whose special kind is none and smart is false
       if (count of every folder playlist) = 0 or (name of every folder playlist) does not contain "Downloads" then
           tell source 1 to make new folder playlist with properties {name:"Downloads"}
           set fpl to folder playlist "Downloads" of source 1
       else
           set fpl to folder playlist "Downloads" of source 1
       end if
       return fpl
   end tell
end makeDownloadPlaylist

on cleanPlaylist(theplaylist)
   tell application "iTunes"
       set idlist to {}
       repeat with i from the (count of tracks) of theplaylist to 1 by -1
           set currentID to database ID of track i of theplaylist
           if currentID is in the idlist then
               delete track i of theplaylist
           else
               if ((location of track i of theplaylist) as text) starts with folder2Scan then
                   set idlist to idlist & {currentID}
               else
                   delete track i of theplaylist
               end if
           end if
       end repeat
   end tell
end cleanPlaylist


on replace_chars(this_text, search_string, replacement_string)
   if this_text contains the search_string then
       set AppleScript's text item delimiters to the search_string
       set the item_list to every text item of this_text
       set AppleScript's text item delimiters to the replacement_string
       set this_text to the item_list as string
       set AppleScript's text item delimiters to ""
   end if
   return do_string(actionid, this_text)
end replace_chars



on do_string(actionid, the_string)
   if actionid = {} then
       return the_string
   else
       set actionid to actionid as integer
       set finalstring to ""
       if actionid = 1 then
           repeat with i from 1 to count of characters of the_string
               set test_char to character i of the_string
               if i = 1 then
                   set finalstring to makebig(test_char)
               else
                   set prev_char to character (i - 1) of the_string --last character of finalstring as text
                   if followed_by_bigchar(prev_char) = true then
                       set finalstring to finalstring & makebig(test_char)
                   else
                       set finalstring to finalstring & makesmall(test_char)
                   end if
               end if
           end repeat
       else if actionid = 2 then
           set firstchar to makebig(character 1 of the_string)
           repeat with i from 2 to count of characters of the_string
               set test_char to character i of the_string
               set finalstring to finalstring & makesmall(test_char)
           end repeat
           set finalstring to (firstchar & finalstring) as text
       else if actionid = 3 then
           repeat with i from 1 to count of characters of the_string
               set test_char to character i of the_string
               set finalstring to finalstring & makebig(test_char)
           end repeat
       else if actionid = 4 then
           repeat with i from 1 to count of characters of the_string
               set test_char to character i of the_string
               set finalstring to finalstring & makesmall(test_char)
           end repeat
       end if
       return finalstring
   end if
end do_string



on followed_by_bigchar(test_char)
   if ((ASCII number of test_char) is greater than 64) and ¬
       ((ASCII number of test_char) is less than 91) then
       return false
   else if ((ASCII number of test_char) is greater than 96) and ¬
       ((ASCII number of test_char) is less than 123) then
       return false
   else if special_bigChars contains test_char then
       return false
   else if test_char = "'" then
       return false
   else
       return true
   end if
end followed_by_bigchar


on makesmall(test_char)
   --when it's a normal character
   if ((ASCII number of test_char) is greater than 64) and ¬
       ((ASCII number of test_char) is less than 91) then
       return (ASCII character ((ASCII number of test_char) + 32))
       --when it's a special character
   else if test_char is in special_bigChars then
       repeat with i from 1 to count of special_bigChars
           if item i of special_bigChars = test_char then
               return item i of special_smallChars
           end if
       end repeat
       --when it's something else
   else
       return test_char
   end if
end makesmall

on makebig(test_char)
   --when it's a normal character
   if ((ASCII number of test_char) is greater than 96) and ¬
       ((ASCII number of test_char) is less than 123) then
       return (ASCII character ((ASCII number of test_char) - 32))
       --when it's a special character
   else if test_char is in special_smallChars then
       repeat with i from 1 to count of special_bigChars
           if item i of special_smallChars = test_char then
               return item i of special_bigChars
           end if
       end repeat
       --when it's something else
   else
       return test_char
   end if
end makebig

on get_selection_index(action_list, theprompt, mult_selection)
   set theselection to choose from list action_list multiple selections allowed mult_selection with prompt theprompt
   set returnlist to {}
   repeat with theselected in theselection
       set i to 1
       repeat with theaction in action_list
           if theselected as text = theaction as text then
               set returnlist to returnlist & i as list
           end if
           set i to i + 1
       end repeat
   end repeat
   return returnlist
end get_selection_index

on clean_iTunes_folder(folder_playlist_2_clean)
   tell application "iTunes"
       set thelists to every user playlist of source 1 whose special kind is none and smart is false
       repeat with i in thelists
           try
               if parent of i = folder_playlist_2_clean then
                   delete i
               end if
           end try
       end repeat
   end tell
end clean_iTunes_folder