It's working great for me but at one point I screwed something up and wanted to install again - I tried booting to the Lion "Recovery Console" and although it booted into it fine, when I choose "Reinstall OSX" from there it told me my machine was incorrect for the OS. I just went back and booted from the DVD I had burned of the install image and did another fresh install and it had no problem with that.
Interesting enough, when I run System Information on the first window is says "Mac Pro Early 2009" for me, but if I then run System Report is shows me as a 5.1 and not a 4.1