Around 8:45 PM last night, my main XPages app stopped responding. The browser would sit there waiting for the server for about 30 seconds or a minute until the server finally gave up and handed out a Command Not Handled Exception. When I first started looking into it, I saw a rogue process taking up the whole CPU, but after killing it and bouncing the server for good measure, the problem remained.
I'll leave out the hour's worth of hair-pulling and cut right to the chase: I had added a doctype line to my faces-config file but hadn't gotten around to removing it. This normally isn't too much of a problem, but java.sun.com became unavailable yesterday (and still is at the moment). Thus, the server was opening the faces-config.xml file as XML and, as XML parsers are supposed to it, it was attempting to fetch the DTD to validate it. However, after waiting 30 seconds or so, it would give up the ghost, spit a misleading error to the console along the lines of "Can't parse configuration file:xspnsf://server:0/database.nsf/WEB-INF/faces-config.xml", and declare that it couldn't handle the command. As soon as I removed the DTD, everything started working perfectly again.
I'm reasonably certain this is Larry Ellison's fault.