The site IS down. Those of you who haven't turned off your PC since the other day still have the DNS in your cache.
This is what happens when you don't pay the renewal for your domain:
Domain name: MAMEWORLD.NET
Administrative Contact:
C, Mark roclobsta@mameworld.net
Mail for details
Exeter, Devon EX4
UK
Technical Contact:
Williams, Zachary admin@ztnet.com
1955 Pauline Blvd
Suite 300F
Ann Arbor, MI 48103
US
734-222-8112
Registrar of Record: TUCOWS, INC.
Record last updated on 14-Feb-2005.
Record expires on 16-Feb-2006.
I expect at some point, he'll pay the renewal fee in the redemption period and it will be back.