I was also looking forward to seeing Mint 12, as unity or gnome shell just do not float my boat at all. To my surprise, and great disappointment, I find Mint 12 utterly unusable with any of its desktop environments, due I think to my graphic card, an ATI 9200SE. Whatever launcher or icon I click on it takes about 10 seconds for anything to happen; even opening the main menu or a right click to get a context menu can take 10-15 seconds. Trying to shutdown takes for ever if I use the GUI, and I have to use the cli from Ctrl+Alt+F1 to do that sensibly and speedily.
I gather after a search that this is a known problem with this graphic card in Mint 12, even though the problem does not occur in Ubuntu 11.10. No doubt updates will eventually fix it, but I can't be bothered to wait for that; I'll stick with Ubuntu 10.04, their best version so far, in my opinion.
Xubuntu 12.04 user, and loving it!