Only using Win 7 x64 as a secondary OS at present, due to WB, IP and Descapes not working in there yet... but Winstep Xtreme works well, as does CursopFX, Fences, ObejectDock and Logonstudio Vista.
Another reason it's not my primary OS is that my AverMedia TV and SoundBlaster X-Fi apps aren't yet compatible in Win 7, when they are, however, I will switch to Win 7 x64 permanently.
Other than that, Win 7 x64 is stable, reliable and faster than Vista x64, so for me it's a definite when it goes gold.... cos by then I'm sure these apps will be working by then. It's only early days yet, and the 3rd party devs will catch up to make this the best edition of Windows ever.