A while back I wrote a very small series of articles about S2. It was intended to be bigger, but at the time there was little interest in S2 and thus my own interest in writing them waned.
The original two, now listed under “More Advanced Topics” were aimed at those who had already got the hang of S2 but wanted to learn some useful techniques and best practices. Later on I added a third article about overriding parts of a layout using a user layer which describes how to override Page::print while keeping the rest of the layout intact. None of these articles are especially brilliant, but I thought I'd link to them here just for the sake of completeness and in the hope that someone will find them useful.