While using Audio Hijack recently to record a free audiobook from iTunes into a DRM-less file to burn onto a CD, I accidentally recorded too much past the first chapter, and stopped it at an awkward position in the book.
In the Info screen for the audio book in iTunes (while it was an AIFF-formatted file), I changed the End Time to where I wanted the file to end, and forgot about it. Later when I converted it into a smaller file, iTunes converted only up to the specified End Time, saving me from having to chop it off later. It seems iTunes will do the editing for you, but only if you convert the the marked track.
[robg adds: The flip side of this hint, of course, is that you should be certain to clear any Start or End settings if you're converting a track and don't want to lose any of the song data.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20061223125114429