I've been using Firefox 3 since the beta versions and have been really pleased with it. It seems to be much much faster than Firefox 2 was with sites loading pretty much instantly. It seems to be a little easier on memory and a lot easier on the CPU for me on FreeBSD.
I really haven't experienced firefox slowing down to a crawl after opening a bunch of tabs like I did in previous versions. It used to happen with few certain sites that seemed to use a lot of java script. I would get the occasional crash on those sites and have experienced exactly zero crashes so far on the release version of FF3.
I like the new location bar a lot. It took a little getting used to because it worked a bit different than I had grown accustomed to but now I don't think I could go back to the old way of doing things. It just makes more sense to search the way it does now.
I'm really thankful for those people who work on all of this great open source software out there. They do a great job with it.