I use a variant of this, for the sole reason that it provides a reasonably flexible grid system that is very easy to use, keeps everything proportional and consistent, and works in all modern browsers.
I don't enjoy spending lots of time tweaking CSS for each site individually, when I can just throw it on a grid and have it looks great.
In my opinion CSS isn't that complicated to use a framework, but that still a good thing if people always upgrade other frameworks and merge them to create a more powerful one!