As with all websites on the internet, we deal with denial of service attacks from time to time. This one has been rather nasty and resulted in some serious downtime for the site. We thank you for your patience as we work to battle this attack - our developers have been working non-stop.
In the war against DDoS, capacity is king - the way to outlast an attack is to have more resources available. We have deployed the services of CloudFlare, who provide far more bandwidth and filtering power than we could on our own. This will help protect the main site somewhat against further downtime, but is far from fool-proof. Unfortunately, it cannot protect our IRC network at all, which is also under considerable attack at this time. We are working to mitigate this attack as well.
You should expect some downtime on the site in the next few days while we clean up some residual damage and do some server house-keeping, as well as fend off further attacks to the best of our ability. We will try to keep both our Twitter and the topic of #what.cd-help up to date regarding the status.

UPDATE: IRC is up and accessible on irc.what-network.net, so please use that address if you wish to connect to What's IRC network in the immediate future. Many users are configured for irc.what.cd (which isn't working at the moment), so be sure to update your server details if that's the case. Thanks!