We've added a TWiki to the web site. Our hope is that the many, many college instructors that are using the book will be able to use it to share notes, tips, and so on. Of course, everyone has access to it so we've put a space for people to write comments, etc. Eventually we'll start adding our own notes.
The configuration is still being adjusted, so consider this the "testing phase."
What is TWiki? TWiki is a web system where everyone can edit a page. "What? That would be chaos!" you say. Well, there is infinite undo and all changes are logged (you have to be registered to make edits). There is access control, so there is some sanity but the system works best when everyone feels free to make changes. The result is a set of web pages that are always up to date.
Or if you just want to read, well that's fine too.