I am the owner of a MacBook Pro and it came with OS X Lion when I purchased it. Last night I decided to purchase OS X Mountain Lion operating system from the AppStore built into Apple. And in general I am somewhat please with the update itself. I use my MacBook Pro for work purposes and Personal Purposes and the inclusion of the Notification Centre especially, I find very useful. I can easily see what tasks I need to do today and mark them off as required.
I have also noticed more magic trackpad gestures and the inclusion of a separate "Notes" section which is much better as I found it very tedious to login to the Mail every time I wanted to check my notes. As its a separate thing now I don't need to load my Emails before finding my Notes.
Additionally Notification center has the ability to post "Tweets" to twitter directly from it. However when I installed Mountain Lion I also expected to have the "Facebook" integration too into "Notification Centre" but apparently this feature will be released in "Fall" (thats Autumn time to us British Folks). So it will be there, just not yet.
I didnt have any trouble downloading or installing Mountain Lion even when I have a separate partition for Windows 7 on my MacBook Pro. Before installing it asks you what partition you want Mountain lion installed to. All my emails, notes, pictures, documents didn't get formatted when Mountain Lion was installed, and it has been a pleasant experience.