Static websites are easy to host and typically very fast.
I developed Cactus because I wanted a standard, easy system that designers at Sofa could use to build and deploy fast websites.
So typical users would be designers that are tech-savvy, want to use templates, but don't like to mess with setting up django or S3.
You can find more discussion about static site generators in this Hacker News discussion.
To start editing and previewing your site type the following.
Then point your browser to localhost:8000 and start editing.
It brings a set of great new features like asset fingerprinting, an asset pipeline, pretty urls, native Mac filesystem events, automatic nameserver configuration, support for multiple deployment backends (Google Sites) and more.
Large parts of the code have been rewritten, accompanied by an extensive suite of unit tests.