Often programs like PearLyrics or SingThatiTune just don't find the song I am looking for, and I have to find the lyrics manually. I found it tedious to find the lyrics in Safari, switch back to iTunes, highlight the song I want to add the lyrics to, open the song's info panel, paste in the lyrics, and finally, close the window. So I wrote this simple AppleScript instead:
tell application "System Events"
set sel to (the clipboard as text)
end tell
tell application "iTunes"
set lyrics of current track to sel
end tell
I then bound this AppleScript to a keyboard shortcut using iKeys (any macro-capable program should work just as well). It will copy any text currently in the clipboard to the currently playing song's lyrics.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080713080757867