I was never a big fan of Gnome. It didn't provide any advantage over the other desktops (in my point of view), so why bother. However, I've tested gnome 3 few days ago, to give it a shot.
I don't like that the first quarter of my wide screen is filled up by extra large window title and application menu.
I don't need to chat so often so I don't prefer such deep integration of the desktop with Instant Messenger. I can imagine the huge dependencies needed due to that.
Tapping my touchpad doesn't click. I had to enable that in mouse settings.
On the other side, I love the rest. Just the way how gnome 3 removed the Start menu is brilliant. In fact it didn't disappear, it is now 'in fullscreen', called Activities. There is no fixed amount of virtual desktops, since Gnome 3 manages them itself, there's always just one empty desktop for future use; and if you move some windows to it, another empty desktop appears automatically. Ingenious.
I think that this is very usable piece of software. I'm looking forward all the new versions.