We're talking about build 5384, right?
This is by far the most stable I've seen it. Plus, my WDM audio drivers work for my Audigy 2, so even though the user-mode drivers for it aren't yet available, I still have sound that sounds good. Finally! Something I could actually use!
I've been saying it since the first time I played with Vista: the security popups are going to drive users crazy. There has GOT to be a happy medium somewhere between where it's at now and where it was. FC5 has a nice feature: you can choose to retain the security context. Of course, then it stops asking for root access, and we're back at square 1.
There's also still a bit of a flicker when it asks whether I want to allow something to run. I'm not sure why this is.
Aside from that, I think it's just about ready to go live. Looking sharp! Media Center looks good, too, compared to MCE's.