Via SmartMobs, at http://www.smartmobs.com/archive/2007/01/05/im_vs_email.html:
The New Scientist Technology Blog: Is IM better for Brainstorming?
The researchers recruited forty two-person teams of graduate business students, and split them into IM and email groups. Each team then had to tackle a business problem facing an auto-repair firm, using only their allocated communication method.
For some reason the paper doesn’t say how long the tests latest. But, on average, the IM teams produced one more idea than those using email. The researchers suggests this may be due to the speed of IM compared to email. Perhaps it also shows that, when it comes to generating ideas, it’s better not to spend to long thinking over your reply, as can happen with email.