The Django folks have started publishing preview copies of The Django Book for free on the Web. This is similar in concept to Beta Books, except that this one's free - you don't have to pay for anything. Excellent.

But far more interesting is the comment and feedback system. They've taken Jack Slocum's comment system and integrated it into the book. Jack's comment system provides comments in context - you attach comments directly to the part of the text you're commenting on.

The results are fascinating. There are already 261 comments on the first three chapters, and it's only been out there for 6 days. I looked over a few of the comments and the vast majority are quality, often pointing out real issues or adding value to the text.

A printed book is easier to read (easier on the eyes, and there's always the read-on-the-crapper factor). It also allows you to concentrate - no IM or email competing for your attention.

But for a technical book, I could see preferring the online marked-up version. This form of navigating a book is pretty interesting - the book is still edited down to a reasonable size and covers the appropriate level of detail, but the comments are there to provide depth where you're interested.