These guys love their work, and it shows. Very enthusiastic, intelligent, and creative. Putting time into the specs pays off.
Managing Director, BoaB interactive
A few weeks ago, I finally received my copy of Pro Drupal Development by longterm Drupal contributors John K. VanDyk and Matt Westgate. It 's an easy read, full of useful tips and discussions, and is IMHO an essential resource for the serious Drupal Guy/Gal.
In true opensource spirit, there's even a public defect list.
I bought three copies, one for me, one for my developers, and one to lend to people, when I'm doing my Drupal Evangelism.