I agree. In an especially technical conversation, I can dive deep in my knowledge before someone steam rolls me with their side (especially useful if someone broad sides me with a question). If it were an email, than the exchange would be far too slow to get anything meaningful done. I rarely come away from an IM exchange not having my problem solved. I nearly always come away from face to face and email communication either without my problem solved or it taking far longer to solve. Granted, this may be symptomatic of how people prefer IM over email but that seems to make the whole argument moot: people will self organize around the most efficient processes.