Nothing, it just collects dust. Friend and I bought one each. The left switches started crapping out at the exact same time, after around 4 months of use as per the gospel you've read countless times before. He lost his nerves and smashed it apart. I adopted the remains intending to replace my left switch with his right, but I'm not exactly experienced with a soldering iron. Besides, really, what's the point, it's going to start acting up again anyway. So now I have two useless G100s sitting around.
Interesting fact -- I plugged the thing in recently and found out the left click has broken entirely. Before, at least it worked one out of five clicks, now it's just entirely dead.
I'd RMA it, but I know it's gonna happen again and I can't do it indefinitely. I'm quite gentle with my mice and I never abuse them, so clearly this is an inherently defective model.