I am very impressed Firefox 3 beta speedy. Right now, I feel it fly like Safari 3.
One thing I don't really like it is "Location bar & auto-complete" because the search result is too wide. And, it really change user experience. For example, I type "d", Firefox 2 shows the first item on the list is "digg .com", but not Firefox 3. I prefer auto-complete to work on url search only.
I also try to see how good its memory management, so I let it run a day and back to my start up page, default google search page. Windows Task Manager show 90 MB. The first start up page is 26 MB only. Looks like there is still big gap to improve in the memory management.
Generally, I give thumb up for it.