My new pastime when bored (and online) is typing names of random fictional characters into Twitter.
No really, there’s a surprising amount of roleplaying going on there. People create accounts under the names of their favourite characters and … go ahead and act in character. I remember seeing this on Facebook and MySpace too. And you’d have to be blind not to see the similarities with logging into an MMO, or any virtual world, under a new character name.
It probably was rife in IRC, webmail and just about any online forum that lets you pick your own name and id when you create an account also. I remember there was once a guy on rpg.net who used to RP being Her Majesty the Queen. I don’t know why exactly but it was very entertaining.
I wonder if wanting to roleplay when given the opportunity to pretend to be someone else is a basic (and emergent) part of human nature — it just never surfaced before because we didn’t have the means to easily take on different identities.