For those lucky enough not to suffer from this bug, or have always wondered why your camera sometimes spazzes out, here's the gist of it:
When you click (mouse left or right button), there is a chance that your mouse cursor will reset to the center of your screen. If this happens while you're panning your camera or turning your character, you will suddenly look up straight in the air, or start to run in the opposite direction. It only occurs in WoW, and it doesn't matter what mouse or other hardware components you're using, and it happens in Windows Vista, 7, and 8.1 (the Windows 8 mouse freeze bug is something entirely different and is fixed by one of the updates offered by Microsoft; please do not confuse the two).
This bug has been around for years and has caused countless deaths for me (falling of bridges/cliffs due to sudden involuntary movement direction changes, misplacing ground target abilities, missing mouseover targets etc. pp.).
I'm not sure if this bug has ever been acknowledged by Blizzard, but a fix is long, long overdue.
Any reports from beta?
Edit: Here are two videos showing the bug: