I used to be an obsessive user of Instant Messaging, back in the day when DOS based IRC was the only thing that would run on my cutting edge 486SX.
I've got back into it fairly heavily recently for a number of reasons, not least the great TipicMe application for my mobile phone that allows me to connect to all three networks (AIM, ICQ & MSN) from wherever I am.
Anyway, I've noticed two distinct differences this time round.
Firstly a large majority of people are connected 24/7, setting their status to things like 'asleep', 'visiting relatives', or 'homework bitches', when they aren't around. This must be due in part to the proliferation of always on connections and broadband. In the past it just wasn't technically or financially viable to keep your dial up connected all day.
Lastly it seems accepted, almost assumed, that everyone uses their real name. My tried and tested online nickname seems to raising more and more eyebrows. I recently sat in a meeting in London where one of the attendees who had chatted to me via ICQ just couldn't stop calling me by my online nick. (See also Matt Haughey: Growing Old Online)
Either way, both seem to indicate that Instant Messaging really is becoming an accepted form of communication for everyone. Not just geeks with odd nicknames.