I just fired up the build I downloaded - very impressive new interface!
Not only does it seem very slick and streamlined compared to 2.4x, but so far it hasn't crashed or given me any errors or anything.
The new interface is much easier to use, I think newcomers to Blender will like it.
Now I just have to figure out these new features and where some of the old ones got moved to...
P.S. - I heard there's also a Linux build, same revision, out there that's also not on the official site, for those who want to try it out early.