My first book (Ship It!
http://pragprog.com/titles/prj/ship-it ) was with the prags and it was a great experience. The book is now in 6 foreign languages editions and I keep getting quarterly checks. The editorial process was incredibly difficult, but that's because they push you to be the best you can.
And the 50% royalty rate is really what you get. I can tell you exactly how many books have been bought and returned, PDFs vs paper books, etc. I've not heard of anyone being able to match the level of information they provide authors.
The build system is also insanely cool. You can render the book on your local box, so you can see how it looks as you go. That's really motivating.
I just published a book on Lulu.com (for a variety of reasons, none negative towards the prags), and it was nearly painless. If you do publish on Lulu, be sure to start with their Word template and that eliminates a ton of the pain. But Career 2.0 (
http://www.lulu.com/content/5925115 ), my latest, has so many more typos, etc in it that Ship It!... it was easier to write, but the editing quality suffered a bit.
Regardless of who you publish with, you'll sell if you market it. Otherwise it won't. You write articles (InfoQ, DZone, etc), you set up a blog, you go to user's groups... you're the main PR arm for your book. You'll get out of it what you put into it.