I just watched the video for 960 Grid System. What a weird idea: constrain the page to 960 pixels and cut it up into 12 columns. When laying out your page, each piece fits into one or more contiguous columns. It might make more sense if you look at their examples.
Naturally, I knew about YUI Grid, but for some reason, watching the video for 960 Grid System helped me envision how I might actually use it. I've never really been good at super complicated layouts without using tables, but this seems easy enough to use. There's even a version of the CSS that isn't limited to 960 pixels.
Anyway, I'm not saying I'm going to convert all my sites, but I do think it's weird that somehow constraining yourself to fixed numbers like 960 pixels and 12 columns leads to greater flexbiliity. Since I'm a fan of haiku, that kind of makes sense to me.