I haven't yet used Win7, so maybe there's a solution to this. I don't think this suggestion might be very popular.. Nevertheless, I'd suggest they allow an option to re-enable the sidebar.
Sidebar's on-top behaviour is a plus point for me on a 1680x screen where maximized windows are bad in (many) cases. I don't have to bang [win]+[space] everytime I wanna see them either; instead a glance to the right of the screen is more convenient for me.
Keep an option to re-enable sidebar..