This is a simple hint. iTunes 5 displays the time elapsed and total song length to the left and right of the song scrub bar, respectively. If you click on the song length, it will change to the time remaining. Clicking on the time remaining, naturally, restores the total song length.
This may be obvious to some, but it wasn't immediately obvious to me. It's nice to be able to see both the time elapsed and the time remaining at the same time. Thanks, Apple!
Mac OS X Hints
http://hints.macworld.com/article.php?story=2005091718044284