I came into the Cafe today just in time to watch a long and messy fsck over somebody's shoulder. I should have asked what they did to freeze the computer up, but I didn't want to seem nosy and annoy the person, so I walked around the room and talked to a few people for a while, until I noticed the individual in question getting up and leaving the Cafe in frustration. I rushed over to the computer to find it in a near-catatonic state -- not completely unresponsive, but very nearly so. Ctl-Alt-F-whatever took a while to clear the screen, but very soon I was able to type "ps aux" to find dozens of Netscapes, dozens of Mozillas, and at least five Galeons rampaging around the CPU. I rebooted after using "killall -12" on all the browsers. In retrospect, I could have simply killed X with a Ctl-Alt-Backspace (or Delete, or whatever.) That would have been a carpal tunnel saver, though inelegant.
Ultimately, when we are done installing apps and configuring the desktop, we are going to make all disk partitions but one read-only, like Jamie Zawinski recommended.