To get people to "try out" the game until launch
I imagine NS2 will likely have a free to play weekend or two once it is officially launched, but in the mean time, it is very difficult to convince friends to plop down $35 for a game they've never heard of which is indie to boot, as many people worry about how active an indie multiplayer game's community can possibly be (though this one is the exception)!
That said, I know if people try this game they'll like it -- is it at all possible to pump out a separate set of keys that people can input on steam that will invalidate after a certain amount of time/when the game launches? This way people can try it out for free, and build excitement.
So far the only way I've been able to get a handful of my friends to buy it and play it is to offer to reimburse them if they don't like it :P
luckily, I haven't had to do that yet, but man, I really want to help out as much as I can.
Is something like this possible? And if it has been mentioned before, I am deeply sorry.