A lot has changed in the last few years-- with modern tools (Skype, Google Hangouts, IRC, GotoMeeting), it is possible to not only almost entirely replicate being co-located, but to even enhance productivity by spinning out ad-hoc co-located teams to solve individual problems.

Need to have a concentrated task force from 5 various departments? No problem, it's a click away-- no need to book a meeting room, take all your gear (disrupting your workspace) and try to collaborate away from your desk in a mutual location.

Currently I sit beside people working that I previously worked on the same project with, but have now slightly diverged from. Trying to come up with a perfectly co-located office plan wouldn't work, because some number of people couldn't help but be misplaced. Not to mention we'd have to do it every few days!