I was very impressed. If you want to live in a world that is well defined and where the familiar metaphors show up no matter where you are, the convergence of the OSX and IOS functionality with iCloud in the middle is where you want to be.
I think the favorite feature(s) for me are the following
1) Mountain Lion Dictation (a boon for us authors)
2) doc sharing with real time updating (Pages,Numbers,Keynote,Preview) through iCloud
3) reminders and notifcations center (the swipe left to bring it up while a full screen app is up would be really nice for my Air.
3) new map and wallet features in IOS
The thing that I can’t understand is why they won’t extend Siri to the iPhone 4. I have dragon go now, and it is somewhat clunky and nuance is the code behind both siri and dragon.