For the first hour or so I experienced unusual performance issues. Now, performance seems to be about on par for me with 10.7. I am on a late 2010 Macbook Pro Core i5 with 8GB of memory.
So far no substantial show stopping bugs. I've had Subler crash on me when starting to convert MKV to MP4, and thats it for stability issues.
On reboot, if you go into Launchpad, just about all of the icons will come up scrambled, but if you give it a few minutes and go back into it it will appear fine.
The gesture for bringing up the notification pain seems to be hit or miss, but this was something that happened a lot in the early builds of 10.7 as well with new gestures so it doesn't really concern me all that much. I think part of my problem is that the trackpads are now big enough that finding the actual right or left hand side corner of the trackpad is hard to do from muscle memory. Once it becomes configurable, I'd like to see if maybe doing it from the top is a bit easier, as I can see that being overall a lot easier to remember.
Thats all I really have at the moment. It seems rock solid. Theres very very few improvements to fit and finish that I can see so far, but this is a fairly early build. When moving a file from one location to another, theres a progress bar on the actual icon, as well as an X on the upper left hand side of the icon to cancel the file move. On start up, if you have Autologin disabled, the Apple logo in the center of the screen does a nice animated move up to the same place on the login screen, and thats really just about it as far as I can tell so far.
Resuming from saved state applications on restart does seem to take longer, but once again, this is an early build, and final performance shouldn't be judged in any shape, form or fashion, as I'm sure we all learned during the beta for 10.7.