There are a couple of great Fresh Aire interviews with the series creator and the main actor (can't remember his name and I'm just lazy enough not to engage my google-fu). If you go to the PBS website, you should be able to listen to them. One of the things that struck me (and someone mentioned earlier in the thread) is that the creator actually took real stories from two of his friends who are doctors to make the first couple of seasons of the show, and uses real interactions between the actors off the set (and anecdotes from their lives) to build the characters on the show. And he continues to use stories from various doctors that write in or he meets.
It's a great show, but I think it started losing a little of its magic due to the angst stuff this season. Still fun.