This generalizes to many  applications – for instance organizing a boycott. Boycotts are useless unless they reach critical mass. (A friend called this “Kickstopper”!). Additionally it could perhaps be worth making a variant “ThunderVote”  specifically dedicated to the voting use case. If you are, for instance, a democrat in a largely Republican area, you might think it's useless for you to get out and vote. But using this site, you could mark who you’d vote for with the touch of a button, but only pledge to actually make it to the polls if a thousand other people of your same political leanings in your district do the same.