I would have liked to have an in depth look at Gnome 3.12, but unfortunately the Live CD I tried kept causing kernel panics every time I tried to launch an application. Here are a couple of screenshots I was able to take:
The Activities overview seems to open quickly. I tried an install of Gnome 3 recently in Fedora and found that there was a significant lag in opening the Activities overview, admittedly on a now-quite-old laptop. I hope this is due to improvements in the compositing engine that might make Gnome more usable for me.
I've seen several people who wrote that they hated Gnome 3 say now that they use it and love it, so I suppose it's a bit ironic that I said I loved it from the start but don't now actually use it. Apart from the performance issue, another issue for me is non-Gnome applications. For example, I use Liferea a lot, but its notifications don't work natively with Gnome and look terrible; in XFCE however, it's fine.
Gnome 3.12 is in Debian Testing. I am tempted to try installing it, because it looks so good, and to see if any of my problems with Gnome 3 have gone, but my current installation of XFCE on Debian Testing is just so usable and stable that I'm reluctant to wipe it.