I've been using a Mac for years - my first was a Performa 630. I can't pretend to be a power user but I did get the developer versions of OS X and was very excited about the move to it. I was a big fan of the upgrade to Snow Leopard too - for me it was the fastest and most reliable version. While I like some of the features and UI changes of Lion I haven't been wholly convinced and was underwhelmed by the Mountain Lion press release.
The addition of a few iOS apps into the system, like Notes and Reminders, feels to me like an incremental update - almost what we would have used to expect in an x.x.x update, not a whole new version. Similarly, whilst I like the multi touch gestures and scrolling between full screen apps there are certain aspects of implementation that baffle me. For example, in Mail full screen, if I write a new message and wish to go back to a previous email - to check something, copy and past etc. - I either have to cancel the new email and save it as a draft or exit full screen mode so I can cycle through the windows. This seems ridiculous - why can't one cycle through windows in that full screen mode? It makes no sense to me to bring in that kind of iOS functionality in a more high-end, multiple windows desktop/laptop system.
I also worry that iOS looks a little tired. I've seen a couple of Windows phones and like the tiles, I like that lots of your most important information is on the home screen. I think the home screen in iOS looks tired. I also don't think the look of it is as adult or classy as much of OS X. I worry about OS X failing to innovate in its own right but merely bolting on the functionality of a system that is, after all, meant to be simple, small in size and highly consumer oriented.