I started an experimentation a few weeks back. Instead of scheduling and holding a meeting in one of eBay's formal meeting rooms, I tried to meet with people in kitchen or cafe (or starbucks across the street from the Hamilton campus) - now this is partly b/c it is getting too tough to find a free room, but I also had a hypothesis that when people meet in informal setting - specially a place that has to do with eating - they are more likely to collaborate.
I have to say the results are mixed so far, on one hand it indeed does make a difference, people seem to be friendlier and more willing to see "the other side" of issue - whatever it might be. However I also noticed that they are more likely to "forget" or back-off from agreements or conclusions that were reached too.
For now I keep doing this as much as I can, at least it gives me an incentive to keep the number of people in a meeting to 3 people max, this alone helps increase the effectiveness of meetings.