Wikipedia will be moving to a new server tomorrow, May 3rd. The change will cause an outage of about half an hour. This outage will occur sometime between 11:00am and 2:00pm PST. I expect this transition to be much smoother than the nupedia transition was (apologies to those who were adversely affected by the nupedia transition), because it is a far simpler site.
Please feel free to e-mail me with any questions.