i've read the dsl book, and i can guarantee you'll learn something from it that applies to any other distro, but it's best for dsl and tc, especially dsl. much of what it talks about that is specific to dsl was engineered by robert, and a good deal of that is relevant to tc, or very close. (we have his mydsl browser which is only slightly different, and called appbrowser.) to say the least, applied to tc the book is a bit out of date, and some things about tc are totally different.
i bought the dsl book primarily to support its authors, my understanding (or misunderstanding) however is that none of the money from the book goes to robert, who in my opinion made a small, usable distro into a fantastic, modular, incredibly unique and notable distro. here on the forum, we've tried to give robert money! he seems to insist on doing it for free, but i don't think the book deal is fair (i do think it's a good book.) that is only my opinion, and if i got any facts wrong i hope someone will correct me on this.