BananaExchange is a GameBanana incentive program to reward modders and other site contributors for their efforts. When you contribute to GameBanana, you receive points, and you can now redeem these points for game keys on BananaExchange. This is GameBanana's way of saying thanks for supporting the modding scene.
I highly suggest keeping this feature hush-hush as a "side effect" of having points and not promoting it on every surface, as I feel it will attract an unruly bunch. People joining, making shitty mods to get points and stuff. I'm not saying that as if its going to come as a flood... but, well, there's one in every crowd.
maybe I'm just too cynical.
I'm not for abolishing it though so here's hoping common sense wins out in the end.