Woot! Downloading now, hoping for Retina performance boost.
It doesn't boost the perfomance at all. Mine's just as laggy as before the update.
One thing they have fixed is when you have more than one full screen app open and you go from one app to the other, there is no more delay before you can actually do anything. I'm very pleased with this.
Anyone know how to activate Facebook on the new mountain lion update?