Gnome 3 is due in the October release of Ubuntu, i've tried it and it is very different from the current version.
There is one new menu that shows your most recent programs and documents, includes a search box and shows a preview of all open windows on the right.
It's still in dev stages so it's far from a finished product, here's a screenshot.
I've tried it on my Karmic installation and it ran ok, below are the steps to try it. Don't worry if you don't like it, it only stays in effect until you log out. These steps are for Karmic ONLY:
Open a terminal.
sudo apt-get install build-dep
sudo apt-get build-dep gnome-shell
sudo apt-get install gnome-shell
That will install the new shell and will also get updated along with your usual updates.
To run the new shell run the following in terminal:
gnome-shell --replace