When I quit my job last year I had a couple things going for me:

1. I had freelanced before in college, so that life wasn't totally new.

2. I had a lot of connections so finding work was never a problem.

3. I had almost $30,000 in savings to even out the slow months.

4. I had iPhone apps that I had built in my free time while I was employed that were making $2k+ a month.

So quitting my job was not risky at all. In fact, I really dislike risk.

All that said, I did come fairly close to running out of money this last August when I had put all my time into the first book and a consulting client didn't pay a rather large sum of money. Now had I not been working on the first book, I never would have used up my reserve cash.