Trying to register on the nuget.org site, first off got a "bla bla username 'steentottrup' is unavailable" (I think that was the message).
Next off I try with another username, but then I get "The email address 'nuget@[mydomain]' is being used." - [mydomain] left out.
No idea why the first error was triggered, but the second one sounds a bit like the e-mail adresse already got registered somehow in step one?
Have you registered at nuget.org before? You could try the forgot password feature and see what happens. :)