Even hardware has heisenbugs!
My LCD was not working: it would just go to sleep when connected to my MacBook. Gloria's iBook would use it (albiet over VGA, not DVI) and I could use machines at work, both analog-over-DVI and digital-over-DVI. I brought home alternate cables, and it still failed.
The other problem is that I've been unable to get s-video or composite video out of my MacBook.
With these problems, I spoke to warranty service on the LCD and the laptop, and both were going to be happy to take care of it.
When I got home, I tried a bunch more cable configurations, and nothing. I tried cycling its power, and nothing. I unplugged it from the AC power for a few seconds, and no-- wait! It worked. What??
In the process, too, I found that now I'm getting s-video out of the MacBook again.
Tomorrow, I get to call both AmEx and HP and tell them that they can probably forget about any required service. While I'm very glad that things are working again... it might have been nice to have nice new units! Oh well, there's quite a while left on the warranties.