Apple already had everyone's billing information from iTunes... you could buy things just by typing in your password... That, for the first time, brought very, very easy payment to the modern software world. That, more than anything, is why there is a business for paid apps.
As long as I manage investments properly and don't spend recklessly, Tumblr has given my family a strong safety net and given me the freedom to work on whatever I want. And that's exactly what I plan to do.
I've done everything from stocking shelves at a natural food co-op, to baking bagels at Brueggers and bussing tables. Then I realized that jobs suck, but if you could get up at 6 A.M. and bake your own breakfast, that is very satisfying.