As to not upset advertisers, Microsoft has issued a big heads up that they are performing maintenance on Microsoft adCenter tonight through tomorrow morning.
The update doesn't seem to be significant. In fact, they said the "adCenter Engineering team will be rolling out some improvements to adCenter." Those improvements are expected to be "minimal internal upgrades." But it may result in "latency and timeout issues within adCenter and pubCenter" console. So be aware.
The maintenance window is between 4pm EST (1PM PDT) today and 8PM EST (5PM PDT) tomorrow, April 1, 2011. It is a very big window, 28 hours to be exact. I am not sure if a 28 hour window is normal for typical upgrades but this is the information we have from Microsoft.
Forum discussion at Microsoft Advertising Community.