I've been using Feisty Fawn since January (herd 2), and it's been reasonably stable throughout (with the exception of the way Beryl broke during the gradual merging of Xorg 7.2). If you want to beta test, go here for Feisty Beta ISOs. This is only recommended if you are not afraid of fixing random things that can go wrong, including X-breakage. I can tell you right now that cd-burning in Feisty is broken for a lot of people, including me. It seems to have improved in that it goes halfway through a burn before quitting, whereas before it would quit before it got started. That's using cdrecord in the CLI. K3B and GnomeBaker still can't burn at all.
On the other hand, there are a lot of new things in here. Wireless roaming via Network Manager is setup by default, and there are extensions for it available for things like VPN (something I'm taking advantage of). Laptop users should like this. There's also the new Restricted Drivers Manager
I'm thinking this might be handy for nVidia and ATi users who want to get desktop effects working and need proprietary drivers to do so. Speaking of desktop effects, Compiz is installed by default, and can be turned on through the System menu using this little dialog:
Finally, there is the new GNOME Control Center. You can modify any settings you want in here, the same way you would in the System menu, but with much larger icons (so if your eyes aren't so great) and in a way that will probably be more familiar to Windows users.
So, anyone thinking of trying out the beta?