Having just played with it on my own, what it does for me is when I bring my mouse into the bottom left corner, it appears. And when I put my mouse in the upper left corner, the multitasking stuff appears, just like when the taskbar is at the bottom. The function of the corners doesn't change when you move the taskbar. Same thing happens on the right - the taskbar is nearly unusable thanks to the charms bar. I have a feeling they're going to say that's not a bug, that's just how Windows works.
I do not understand what I do. For what I want to do, I do not do. But what I hate, I do.