Security

All previous versions were just release candidates, whereas this release is the real deal.
I used the Nightly Tester Tools to override my extension versions so that they will work (somewhat) properly with Firefox 3.0.

Any extension that does not have a secured update location was removed from my laptop, on purpose.
As more people adopt 3.0, I suspect more extension authors will start using secure update locations, because, by default, 3.0 makes it difficult to use non-secure updates.

All in all, this version seems to use much less RAM than FireFox 2.0 with general use.

I would wait for mirrors to get FireFox 3.0 Beta 1, but it does seem to be on the primary host right now.