Does Birth control cause weight gain?

I have been contemplating getting on the pill for the past year. However, I have heard that it causes weight gain. I have also heard that it causes some girls to go up as much as 2 bra sizes. (from a B to a D for example) I do not want any of the above to happen. However, I do not want to get pregnant either. Condoms are not always effective. I really want to get birth control but the chance of possibly gaining weight always deters me because I am scared of gaining weight. So my question is, to those who are on the pill or have experience with birth control, do you really gain weight when you take the pill, and if so, how much typically?