I refused to update for the longest time when Ubuntu switched to Unity, but then I got a new laptop and figured I'd give it a shot first. I was pretty set of just using Mint but really wanted to give Unity a try before switching. I was surprised that I actually sort of liked it, especially once I learned the keyboard shortcuts. My task bar always got cluttered with lots of windows in Gnome 2, and their order wasn't consistent which was a minor annoyance. Realistically, Unity feels a lot like Windows 7 to me (though I've only used Windows 7 briefly on other people's machines, I really liked the UI), and it got rid of all the clutter. I like that Gnome Do is essentially integrated into Unity, and there are some other nice features as well.
That said, I haven't seriously tried Gnome 3 yet. I installed it and loaded it up, and then did a wtf when I couldn't really figure out how to use it and wondered why it was so ugly before switching back to Unity. It felt like a very incomplete product. I've since read that you need to use a lot of add ons (or whatever the correct term for them is) to make it more usable, but at this point it's not worth the investment in time when Unity works well enough for me.