I just bought a game that doesn't exist yet. Curiously enough that is all the rage these days. I assume that it has to do with the typical game hype cycle, where every game is great before it is released, and sucks as soon as it is released. Thus it becomes easier to sell a game before it is released, or even created.
Having said that, I was well willing to pledge $10 to Banner Saga on Kickstarter, because tactical RPGs on the PC aren't exactly plentiful. Best case scenario is me getting a game I want for $10. Worst case scenario is Banner Saga never getting made and my $10 just ending up as a faint signal to the game industry that "Hey, people would like to see some tactical RPGs on the PC!". I'm not likely to spend huge amounts on multiple Kickstarter projects yet, but I'm okay with trying it once in this case and see how it works out.