I just updated my Arch Linux installation and it has Gnome 3 by default. I followed the Arch Wiki about Gnome 3 for the installation and it went smooth.
As for the first impression, it is at least much better than Ubuntu Unity interface. For one thing, it does not have the annoying Global Menu. However, I still prefer the old Gnome 2 interface. Anyway, the new interface is at least tolerable, not like Ubuntu Unity. I think I can get used to it soon even though I still miss the Gnome Panel Applets.
I tend to think Unity is one way for Ubuntu to differentiate it from other Linux distros, let's wait and see if that really pans out well for Ubuntu or not.
Notes added on 17 July 2011: however, the problem is with the Nvidia driver. Gnome 3 just does not work well with the Nvidia driver right now under Arch Linux. So I have to switch back to the Fall Back mode.