So far I really like it. I haven't had the time to spend on it like I want, but this weekend I will tweek it and play around. I love iMessage and Message integration on my iMac. I've just got to get it to work seamlessly. I've got messages coming in and not coming in as quickly and then some getting skipped and too many threads on my iPad and iPhone from the same person. It's weird. I've got to make it work better.
I like the Notification area, but I have to learn more about it. I thought I would get all the Notifications on my iMac I suppose it makes no sense for App notification to display on my iMac.
I like Notes on my iMac and iPad and iPhone being the same and updated as soon as you make new ones or changes.
I appreciate how much better the updates for Numbers is. I use it to create my monthly budget and it wasn't so seamless in updating on the iPad and iPhone before, but now with iCloud being the glue, everything is updted at the same time on all three devices.
I have to get used to he new way Safari work with Google search being integrated directly into the address bar. It was a good idea.
I'm sure there are other things I have to learn that I don't know, but yes, so far I love the changes Mountain Lion brings.