Dan, it's free to sign up. They do let you do color, but as far as I can tell you have to go all color or all b/w for an entire book. I've got a couple books at our office that we printed with lulu and the quality is *very* high. You can do hardcover if you like, I'm going for just a regular 'softcover textbook' feel with the work I'm doing.
The best technical books out there are O'Reilly in my opinion, so I'm aping their style and layout as much as possible.
Working on a new "beta" version tonight, I'll let you guys know when it's up. The last one was 6x9 which is more of a trade paper "fiction" layout, I'm doing the next revision at 7.4x9.6 which is more like a paperback textbook.