Thinking out loud.
The upgrade to Mountain Lion has been smooth. There are a lot of nice additions. In some cases, it feels like some key things were left out regarding iCloud and integration with other devices. Maybe those will be filled in with the release of iOS 6.
In the process of upgrading, I also moved back to using Mail, Calendar, Messages and Contacts. I've been using Google for interacting with most of that, but decided to give it a rest. Of course, that meant spending some time moving some things around. We'll see if it was worth it.
That said, my other computer completely borked on the install and I have to take it into an Apple store to be evaluated.