[Update, June 2011: for some reason this page has been getting a lot of hits recently. Gnome 3 has been released, people. If you want screenshots, visit the Gnome 3 site for screenshots of the finished product.]
I found some screenshots of the new Gnome 3 mockup on the Debian forum. (The Gnome 3 release has apparently been delayed to accommodate the changes.)
I'm looking forward to using Gnome 3. The present desktop model in Gnome dates back to 1995. Time for a change. I've used the Gnome 3 shell in Ubuntu and (briefly) in Fedora and liked it. In both distros it caused computer lock-ups, but I'm pretty sure these were due to using it with Compiz running at the same time. Now I'm running Debian Stable, where the Gnome shell is not available. If Gnome 3 comes out in March, I guess it will miss the next release of Debian Stable too (due around the end of the year). Sigh.