Over the last 20 hours, freenode has been trying to deal with a massive botnet attack. Over the course of that time, they removed the irc.freenode.net server to chat.freenode.net. Service has now been restored to irc.freenode.net, but freenode is considering a permanent transition to chat.freenode.net. In order to prepare for whatever changes freenode may make, I have adjusted references to irc.freenode.net on the wiki to point at the freenode website (http://freenode.net/) instead. For more information, or if you have trouble connecting to freenode, please see the news on their website at http://freenode.net/news.shtml
I would encourage anyone who maintains websites or documentation to update their information in a similar manner. While we can expect irc.freeenode.net to remain operational for a long time to come, pointing to freenode's website rather than a server directly avoids dependency upon that server, and users will likely experience better service by visiting freenode's site and selecting a server that is geographically close to their location.