UPDATE 06/01/14 08:25am CST: The migration has completed. There was less than five minutes of downtime for some sites. Most sites had no downtime at all.
We've had intermittent problems with a single webserver over the last month (see our previous status update), so we have decided to migrate the sites it hosts to new hardware. The process will start at 5:00am (that is, very early Sunday morning) CST. Downtime is expected to be brief, around five minutes.