They do have a partnership with a print-on-demand company that donates 10% of the revenues, but it just concatenates articles you choose into a book: http://en.wikipedia.org/wiki/PediaPress

There is also a user-driven project to organize Wikipedia articles into books, although they currently just use the articles verbatim as chapters, which doesn't address things like redundancy between articles that makes sense when they're articles, but should ideally be removed if they were going to be printed as book chapters: http://en.wikipedia.org/wiki/Wikipedia:WikiProject_Wikipedia...

Here's an example one: http://en.wikipedia.org/wiki/Book:Compiler_construction