I have an alt on Facebook, does that count? His name is "Carl Baxter"
It was sort of a joke from a D&D campaign. Our party was wandering through a dungeon, and stumbled upon some guards. Instead of fighting immediately, my bard cried out something like "Oh, thank God, someone who knows their way around! Can you tell us where Carl went?"
Twenty epic bluff checks later, and we had spun this whole character, Carl, who worked with Tiamat Textiles as a Dragonwhisperer. Needless to say, the guards didn't know him (although if I remember correctly, one guard didn't want to admit to his ignorance, so pretended he had heard the name before), but we used the time spent in conversation to position the party strategically, and managed to capture them.
That night, I created a Facebook account for him, and every so often I write on the party members' walls in character.
Never bothered making an alt on this forum though. Just seems like a waste of time, and if I use it to troll, and somehow get found out ... well, that just makes me look like a jackass too.