So that's 2 of us...
There are way more than two people seeing this issue - some get an all blank window that they can refresh, some get a screen freeze (computer wedged) or kernel panic (gray screen of death) which require a power off/on to reset the computer.
Possibly due to a recent change in how full screen works, in any event the only thing that we have in common is using a Mac. Problem happens with Lion (10.7) as well as Snow Leopard (10.6), iMacs as well as Macbooks and Macbook Pros. This problem just started about two months back, and is now a very repeatable problem. For one of our systems we've completely given up trying to "tab out" by using windowed mode - crashes our iMac each and every time.
Multiple threads on this problem already, one of which is http://us.battle.net/wow/en/forum/topic/4662236502
Sometimes running the Launcher's Help menu item "Verify/Repair Game Data" seems to help, at least for a while. For me it does not fix the problem, only makes it go away for a while or change symptoms.
I'm hopeful that since this is now being reported on 10.7 (the most current Mac OS X), that Blizzard will spend a little time on the issue. It's a real frustration that many folks can no longer switch reliably between full screen and windowed mode.