I, like most people, am hesitant to use beta software. It's usually buggier than a termite mound and crashes more than a sauced-up Teddy Kennedy.
However, I've been using the latest beta version of the Firefox browser (available here) and I must say that it, even in beta form, is a marked improvement over Firefox 2.
It's far more stable and it doesn't link memory like a sieve. I've had browser windows open for several days and then taken a look at my system resources and found Firefox 2 claming 900+ megs of RAM. That's not the case with the Firefox 3 beta.
There are some plug-ins which don't work with the beta, so if you're dependent on them for your Web browsing, don't switch yet. However, if you're using Firefox 2 right now, there's really no good reason not to go ahead and upgrade now.