Speed is generally very good - certainly an order of magnitude faster than the beta. Live window dragging is a smooth as silk, window redrawing has a satisfying snap to it and because of Quartz's multi-layered window server, window contents don't have to be redrawn as other windows are dragged over the top of them. Of course you can now happily let files download in the background with more peace of mind than under OS 9. Oh, and it hasn't crashed once, after 10 days of continual testing. Individual applications have crashed, sure, but the OS allows these errant processes to be simply terminated.
Application support is, of course, the big question.
There seems to be a lot of worry about big players like Adobe not having any of their apps Carbonised at the time of release. However, it's also claimed that it has been waiting for the Carbon APIs to be 'frozen' on this release before really cracking on with the task. Most commentators are pointing to a Macworld New York roll-out of the big names in July. This argument might have held water if other companies didn't already have completed versions of their applications now. Macromedia has really put one over on Adobe by having Freehand 10 ready for OS X now.