From the iTunes 7 release notes:
Gapless Playback
Live albums, classical works, or any work that sounds best when it’s continuous, now seamlessly transitions from one song to another.
I’ve been waiting for this one forever. I have a few albums that are like this, but when I listen to them in iTunes, I get an annoying skip inbetween tracks. But in order to get this on my iPod, I’m sure I’d have to buy a new one…