By which I mean; if you pick a topic to turn into a book your likely to have articles of a wide range of quality (from featured status, the top, to stub, the bare minimum).

Couple that with potentially disparate styles of writing and it can become difficult to stitch several articles into a book form.

Not that people don't do it; the volunteer email support service regularly gets people complaining about the $50 "text book" they bought of Amazon simply being Wikipedia articles.

It's always been in the back of my mind to try and do something like it though; perhaps an "obscure topics" book with some of the more interesting articles put into it.