Look...I'm probably the biggest MS supporter here...but I'm certainly not going to be the first one to point out that even when MS DOES release a product, it's till buggy and potentially damaging. So I certainly ain't touching any MS beta object that I don't have to (or that doesn't come in a zero-footprint trial, like their new beta search engine).
Second, system restore doesn't save you from the time you could lose, the agrivation, the settings you'll potentially have to go back through and reconfig...and most importantly, sys-restore doesn't protect you from files that a beta has destroyed.
Anyway, unlike some other people, I don't have the time to dork around with applications that don't fully work and will potentially lead me to a system-restore or collapsed machine.