We've finalized a cover for the book, based on Rob Suisted's image of a Black Tree Fern. Here it is:
I've started on the beginnings of a web site for the book. There's still many design issues to sort out, but for now I wanted to put some of the book code online, to get feedback on the presentation of that code. Take a look here to see the code from Chapters 3 to 12, and send me comments at mtk AT man7.org, if you want.