Setting out to write a book like this - did you just decide to do it or were you approached by a publisher? And was it hard to get published - I hear stories that unless you know the right people you have to be very lucky to get anything into print.
I sent a proposal for the idea to the publisher and they accepted (although the final book doesn't quite follow the same lines as the proposal). I found that it's not so much knowing the right people, but knowing the right content and having an idea of how you want to present it.
Most technical publishing houses are always on the lookout for ideas, if you have one that fits with the sort of books they publish they're almost always willing to talk. Most have an email address or a web form where you can submit your proposal, making it very easy to get the ball rolling. Once it's rolling though: it's hard-work, but (like writing good software): it's also a lot of fun.