As long as I can continue to purchase and download software as normal I couldn't care less about an MS app store.
The second they try to lock down Windows so you must use their app store, I'll be gone from the Windows platform and won't look back.
So, whatever. Don't care. If Microsoft decides to shoot themselves in the foot trying to push this, they are easily replaceable.
I really don't think MS is that quick to hurt itself, I think what they are looking to do is monetize development on their platform just like Apple does. To develop for the iPhone/Pad you need a Mac and the piece of hardware you want to develop for plus a developer's license, not only that Apple gets a cut of every sale. For Windows all you need is a copy of Windows and MS sees no money after that unless you get their development environment.
What I do see MS doing is pushing this as the best way to get software and downplaying anything Joe Internet user downloads, maybe going so far as to disable UAC for all app software to make it even more painless.