FF 1.5 and FF 2 was killing me on the desktop, for exactly those reasons Benson lists. I always kept it up and running, and it would eat hundreds and hundreds of megs after a while, until I had to shut it down (actually I kept several running, in different accounts - to keep some of those cookies separated). Thus losing my carefully collected pages.

FF 3 is much better. The memory leak seems gone, or at least much better. It's also much faster on e.g. Google mail, where (due to a slightly higher round-trip-time at my site than what's optimal) the ajax/javascript slowed everything down something terrible. 15-20 seconds between clicking an email until it was scrollable! (in pre-FF3).

Still, it'll be interesting to see where this chrome thing will go.