I'm using WoW in windowed mode because I have 4 windows tiled to exactly fill the monitor.

A few work arounds:
1. Sam's workaround above - ugly, suppose it could work.
2. Play with 2 monitors and put all the wow windows on the monitor without a taskbar.
3. Exactly tile the windows to meet the taskbar (turn off autohide) so that the taskbar is always visible and doesn't share space with the windows.

This is really a flaw with the new version of windows. The OS shouldn't presume to have something more important than the programs running on it.