+1 for the need of a better task switcher. Even Mango is light years ahead.
On a side note, it seems that Win8 tablets won't have the mandatory hardware buttons of WP, so the experience between phone and tablet won't be that seamless. No big deal, but I think they missed an opportunity here.
As for the desktop, I don't think we will have an MS sanctioned start menu replacement, or even just an option. I'm only guessing, of course, but if they introduced that, everybody would just end up living entrenched in the desktop environment (like everybody wanted to turn off the UAC in Vista) and Metro would become a lonely place like Media Center. Goodbye Metro apps, goodbye store, goodbye developer opportunities. I don't think they'll let this happen.