This will probably be useless for 99% of you, but I've been using it for a while and it can be useful sometimes, since my computer is crap and it takes a while to initially load when I log in.
1. Log into WoW, stay on the character Xfer screen
2. Hold Alt, press left Tab and quickly press Enter...It'll minimize WoW, but it'll start loading. Press Alt+Tab again and it'll automatically re-maximize WoW when it's done loading.
Like I said, my computer is a piece of crap and it takes a minute or two to load...I'm extremely impatient, and I'de rather be browsing MMOwned or something during that time.