A week ago, while doing rogue skillups w/ lockpicking at around 3AM, I had no guildies on, and didn't see anyone around to cure the poison debuff i had that lasts 7 days if you don't go to tarren mill to get it cured. I hit up the AH in Orgimmar, then picked up my mail right outside.
So, i figured, heck, i'll just get on my paladin until tomorrow when the server isn't completely dead. I afked, grabbed a soda, and accidentally pulled up the wrong WoW window, thought "odd, i got DC'd". Logged in, and realized that i had kept 2 WoW windows open from 2boxing earlier. My paladin was logged out at the exact same mailbox, and to my left was my rogue. I cleansed him, giggled... Then I thought about it, tossed over a kings, and yup, it stuck too.
This morning, I had my buddy invite me to the group, i opened my 2nd window of wow, logged into the same account, and was able to toss an hour motw on the paladin. Logged off, got a 60min fort on the paladin.
I know none of this is game-breaking, but i was pretty stoked to have my level 32 rogue running around w/ fort and motw... it made soloing and picking locks in angor fortress in badlands a lot easier w/ 600 more hp.
So, TL;DR version:
Log in character1 in first WOW window, move him to where character2 is logged out.
Log in character2, buff character 1.
Because I keep all my characters hearthed to the inn in dalaran, it makes it pretty easy to do this every time i log into my lowbies.