I’ve been running it for a while now and really appreciate some of the new features. The dictation feature is kind of cool, but has the drawback that it requires an internet connection and sends your dictation off in one big chunk. It’s reasonably accurate from my very basic tests. Notifications with VIP’s in mail is a nice feature. With regards to tabs in the cloud, I’m pretty sure these only work with other OS X 10.8 Macs using your iCloud account at the moment, and we will have to wait for iOS 6 for that functionality to cross over to iPhones, iPads etc.
The biggest selling point I can see for the average Mac user is the added security. Using the default security setting of “Mac App Store and identified developers” makes the platform VERY secure, to the point that I would suggest OS X 10.8 users not use anti-virus software (because these programs can potentially open up significant security holes, and they act like a parasite, sucking up resources and slowing everything down).
Also, it’s only $20, so that makes it a no brainer. For the average Mac user, I think @rooeytoo‘s approach is smart, usually the first few updates after commercial release iron out the majority of glitches that may still be out there. I haven’t experienced any major issues since installing the release build.