I haven't used Windows 8 yet, still running Windows 7... however, the idea of a full-screen start menu seems annoying. I like the current start menu because I could be browsing through something, maybe watching a video, and it'll be pretty quick to simply press the windows key and search for something, load up some music, a web browser, etc... It's trivial, and fast.
I'm actually wondering how deeply you'd be able to set up this full-screen start menu. I have multiple monitors, so would I be able to have it pop up on a side monitor instead of my main monitor which might be running a game, or possibly a full-screen video?
I also think it seems un-nesscessary, and distracting. I never use Windows Media Center for the same reason. It's all flash & no substance.
My guess is that I'll have the same experience with this new start menu... although who can say until I actually use it.
On first glance, though, the whole thing looks kind of dumb, and I'm glad there's stuff like Smart8 out there for people like me.