A few weeks ago, I installed the latest version of the Gnome Accessibility Toolkit (Gnome-AT), and while I never quite got it to work the way I wanted to, it didn't seem to be doing any harm. I figured once I got to the point of showing the client the work we'd talk about accessibility issues. (Many of her clients have low vision problems, so making the site super-accessible is super-important. I'll have a post soon about making _specific zones _of your websites auto-sizeable in an elegant way with jQuery.)
It turns out that it wasn't working because I hadn't stopped and restarted X. So, when I did that after installing some new fonts, everything went kablooey. The most tragic was Emacs, which grabbed the mouse and keyboard and never let go. Very annoying. I had to kill X remotely, logging in through my Palm pilot (which isn't much fun, believe me.)
The problem with very stable OS's is that when they go unstable, the events that caused the instability may be separated from the experience of instability by days, even weeks. In this case, four weeks. It wasn't until X had died for the third time-- this time is a screen session I had accidentally started it in, but which luckily preserved the output of X's error log-- that I finally saw Emacs spitting out all these "at-lock-FAIL" warnings and wondered what the heck those might be. A quick un-install of the accessibility components and I'm back up and running, but man, that was annoying.