What Brink was trying to say, is that if you upgrade to this non-official build, you may be unable to automatically get the official build when its released and have to reinstall. So please be careful if you decide to install this.
There are a number of known problems with this build from what I've seen in the demos.
* Start Menu crashes frequently
* Task View has various issues
* Various apps don't work
* Spartan not included
There's probably others, but if you're going to use this, i'd suggest just installing it to a separate VM, and not your current system.
I plan on installing it on a separate partition on my VM. There is no way I would upgrade to that over 9926. Thanks for the information. :)