I find autohide for the task bar to be supremely annoying. I prefer instead to uncheck keep the taskbar on top of other windows. This will let the WoW window cover the taskbar. You can mouse all the way to the edge of the screen and never have the taskbar pop up. If you need to get to the taskbar, you can hit a variety of different keys to bring it to the front (i.e. the Windows key, ctrl+esc, etc.).