Confirmed: The problem is with mydomain.com
See here: http://twitter.com/#!/search?q=%23mydomain

Also, they're starting to acknowledge that there's a problem:
http://twitter.com/mydomaindotcom

Even if mydomain fix the problem immediately it's likely that it will take several hours for their change to propagate across the internet.

We do not recommend that people update their host files. Some of the instructions in this thread for doing so are incorrect and you may have problems connecting to utopia in the future. Please do not update your host file.