I think 6 months of runway is not enough. People usually have 6 months of cash cushion to bridge until the next job. But you have to refine a business idea, develop the product, market it, sell it, and turn a profit that can replace your old salary. 6 months are far too optimistic. Two years are more realistic.
If you can't wait for the startup bug, why not do it on the side for now?
My post was rather misleading. I have been working on the side for the past 3 years now on iPhone apps. I have 6 months of savings, and I have a daily income from existing iPhone apps that matches my current corporate job. I'm releasing a new app in a couple weeks that should hopefully boost that daily income significantly.
If you can't wait for the startup bug, why not do it on the side for now?