Since I've started today writing about UI issues, I might as well continue. I stumbled across a satirical review of Windows7 on kuro5hin (who knew kuro5hin was still being updated?) which highlighted one or two new window management features:
You can drag a window to the top to maximize it, which is surprisingly useful. Dragging it to the side maximizes it to use half the screen, which is great for two Explorer windows for moving stuff around.
I've always found old-windows' right-click-on-taskbar menu items for auto-arranging windows very useful and wished that stock GNOME was as useable (you can get a bit closer with Devil's Pie. I might still one day resurrect my own window manager idea). This is probably no more discoverable than the old way, but useful none-the-less.