As the server has changed IP address, some users are having some trouble reaching the site. The following advice has been posted on their front page for people experiencing a problem:
1. Check your hosts file. If you edited it when we changed servers before, it'll still be forwarding the what.cd domain name to the old server. Just remove the what.cd lines, and all should be well.Note: Their news article contains an error, which I have corrected here. ifconfig is not a valid command on Windows XP, and I can only assume they meant ipconfig.
2. If that doesn't work, flush dns. In windows, you do this by going start -> run, typing in cmd, then typing in ipconfig /flushdns.
3. If the above two methods have no effect, then your problems are most likely caused by caching in your DNS servers. They'll be sorted out automatically in the next 12 hours.
Note 2: Someone in the comments asked about how to check the HOSTS file. Here's a great article on doing just that. http://www.mvps.org/winhelp2002/hostsfaq.htm#Editor