On ServerFault we have noticed alot of people naming their accounts Server fault,, Moderator, or new today Deleted account. This could lead to some confusion and I would like to request they be blocked. Also though I haven't seen it, I wonder if someone could sign up with an expletive or non appropriate username?
If you think a particular user name is offensive or confusing, just flag one of the user's posts with a message to the moderator.
They have all the tools required to deal with such behavior.
The trouble with a black list, is that people can constantly figure ways around it.