And now I'm posting this from the 6.1.7000 build that's doing the rounds, which is probably the proper beta. Initially installed as an upgrade over Vista, which didn't go so well: the performance was appalling and Outlook wouldn't connect to the remote Exchange server. Format and fresh install and it's all looking a lot better.
The new taskbar is ace, big improvement over the Windows 95 one. Performance seems good but obviously it's a clean install so that's an ongoing thing. Other than that there's a lot of tweaks and refinements to the Vista UX, which are very welcome.
Office 2007 and Visual Studio Team System 2008 both seem to work fine.
It's installed on my work laptop (I also have a desktop which is still on XP SP3 for legacy support reasons) so I'm using it for real unless something goes horribly, horribly wrong. Woo.