Previous Kickstarter here. I'm not a lawyer, this isn't legal advice, blablabla.
You might want to have something in place (S-Corp or LLC) before your Kickstarter launches.
You can be sued for any number of things other than the obvious. If your product is significantly delayed and you don't deliver on time (been there), you can be personally liable if you don't have a structure in place.
Also note that an LLC itself isn't enough to protect you. We did the whole legal zoom thing and one day a lawyer asked us about our operating agreement. Naturally, we responded with "Whatchu talkin' bout, Willis?". She informed us that an LLC without an operating agreement isn't really a legitimate entity and won't pass the "corporate veil" test if anything should go down.
TL/DR: Talk to a startup lawyer.