In the cases I've seen 'open offices' implemented, its been to cram more people into the same space, and save on real estate costs.
This isn't what I see at all. Instead, I see basically two kinds of people: one group is the kind mentioned here, who use IM to talk to people a few desks over, but the other group is loud-mouths who just love to get up and go talk to someone in an open area, and drone on loudly for 30-60 minutes talking about something that could have been handled by email or IM, or perhaps even in a meeting in a conference room, rather than disrupting everyone around.
It only takes a couple of these loud-mouths to make the open work environment miserable for everyone else.