I have a slightly different perspective from Steve here. Instead of quitting your job tomorrow and going into panic mode because there's bills to pay and mouths to feed, I take a different path.
Instead of thinking "Either Or" I think "Both". Meaning, why not do your job and pursue what you love, at the same time. It could be based on the fact that I took the path of quitting my job to do what I love when I was younger and two years later I almost ended up bankrupt, but nowadays I advocate a much more practical and less intrusive method of making the transition towards doing what you love for a living.
I wrote an article about it if anyone's interested:
Making the Transition to Doing What You Love for a Living | Inspired Money Maker - How To Make Money Doing What You Love
This path has worked for me. Perhaps it might work for some of you who aren't ready yet to quit your job tomorrow.