I run Vista 64 RTM as my primary OS. Not in a VM, but on my Dimension 9200 with 4 GB of RAM. I must say that I am very impressed with the driver support on it. Everything works, from my GeForce 7900GS (some major glitches with the driver right after RTM, but they’ve been fixed now) to my soundcard (a C-Media… – though it can’t pipe mike/line-in sound directly to my speakers… WTF…).
I’ve had a lot of iTunes crashes (until 7.1 came out, that fixed the problem) and VMWare Server still isn’t supported on my platform at all (though that’s a Vista thing I believe, not a Vista 64 thing). 32 bit apps run great (you’d never know they weren’t 64-bit), with the exception that Visual Studio.NET 2005 can’t do edit and continue on 64-bit apps (wtf?).
Other compatibility issues: some browser plugins (Flash, I’m looking in your general direction) aren’t compatible with IE7 64-bit, so I have to use IE7 in 32-bit mode most of the time. Not a big deal, though.
What I was most surprised at was the memory utilization. ALMOST ALL OF THE TIME, NO MATTER WHAT I AM DOING, over 2GB of RAM is used. I chalk a lot of this up to SuperFetch. And I must say that SuperFetch uses the memory WELL. Apps launch incredibly fast. VS.NET 2005 comes up (even with the .NET 3.0 CTP designers all installed) in about a second. So far, I’ve been extremely pleased. And yes, for a developer, 4+GB on a desktop with Vista is definitely worth it (especially if you also consider that apps intrinsically use more memory if they’re 64-bit native).