Firefox 3: Power User's Guide to Firefox 3
It seems that lifehacker.com puts out some great information. I ran across this on my iGoogle.com page a few minutes ago. I've been using Firefox 3 for quite some time now (as a supplement to my normal Firefox 2, Safari, and Camino browsing habits). As the releases neared release, they kept getting more stable. Now that I've had it installed for a few hours, I have to say I'm pretty happy about it.
I've also installed Flock 2 Beta 1... a great browser based on Firefox 3 if you're heavily into social websites and sharing your media (like photos with Flickr, for instance).