Already have it installed. I like it, but of course, I was an early Win8 adopter, so no surprise there. Centrafuse runs just fine on it. Biggest change: boot to desktop. Does what it says. Bad news: may not be included in final production version. Start button is back, but not what you think. It just goes to the Start screen...BUT, there are a lot of new ways to organize that screen. Again, I like it just fine and never missed the start button in the first place.
Search is very nice, as are a lot of other smaller improvement. Install was seamless and literally just a couple of clicks. Kept all my apps, although there were one or two that had to be reinstalled/re-configured. I wouldn't do it on a production machine, but if you're a Win8 user already, or thinking about it, do your homework and give it a try.
What's important about this build is that it almost entirely encompasses changes requested by users. Some I agree with, some I don't but it's still nice to see the response. With yearly (free) updates scheduled, it reflects a real change in how Microsoft is approaching its core platforms. Visual Studio 2013 preview was also released today. LOTS of really neat additions to support the new Win8 eco-system. I believe the ultimate goal is to create a unified platform across desktop, tablets and phones that share the same core code, and allows developers to write once and deploy everywhere. Nice marketing terms, and it certainly won't achieve that anytime soon, but its a worthwhile goal.