A WebmasterWorld thread reports Microsoft adCenter advertisers receiving emails saying that they may undergo an account audit. I suspect these account audits are random and allow Microsoft to see if there advertisers are complying with their terms of service.
The email also had a promotion aspect, encouraging advertisers to opt in to their contextual ad network.
Forum discussion at WebmasterWorld.

Comments:
Franck S
01/25/2007 04:36 pm
I found your site while searching for feedback on MSN since I've heard from many top affiliates that MSN had higher ROI for them than Google and Yahoo! I will sign up for an account.