Rich Hickey works on Clojure full-time for free, and he's asking people who get something out of Clojure to contribute some cash. $100 is less than I spend on random books and crap over the course of a year, so I gladly chipped in.

Clojure doesn't make me any money, I use it for hobby websites that actually cost me money every month just to keep going. But it's so much fun I think $100 is small price to pay, if it keeps Clojure development going.