A great article by Ben Brooks called Fragility of Free, well worth a read:

The fragility of free is a catchy term that describes what happens when the free money runs out. Or — perhaps more accurately — when the investors/founders/venture capitalists run out of cash, or patience, or both. Because at some point Twitter and all other companies have to make the move from ‘charity’ to ‘business’ — or, put another way, they have to make the move from spending tons of money to making slightly more money than they spend.

I also like to, and do prefer to, pay for things.

See also: Developers, a Love Story