Static site generators are popular these days. For small sites, the ability to quickly author content using simple tools is key. The ability to use lower-cost (even free) hosting, often without any dynamic capabilities, is good for trying to maintain a budget. For larger sites, the ability to serve content quickly and cheaply is beneficial, and since most pages are read far more often than they are written, generating a full web page to store on the filesystem can improve performance (and lower costs).
For me, I like the convenience of using Github Pages to host project-oriented websites. The project itself is already on Github, so why not keep the website closely tied to it so it doesn't get out-of-date? For an organization like the Chicago Perl Mongers, Github can even host custom domains, allowing easy collaboration on websites.
It's through the Chicago.PM website that I was introduced to Octopress, a blogging engine built on Jekyll. It's through using Octopress that I decided to write my own static site generator, Statocles.