My problem with Taskbar at the Bottom is that the mouse pointer has to be aligned with the Taskbar to make a selection. If you are not careful the pointer disappears off the bottom of the screen. That doesn't happen if the Taskbar is at the top. So to make a selection you just jam the mouse to the top of the screen and slide left or right.
This saves me 250 milliseconds per selection. It adds up. ;)
What do you do with all that extra time?