First off, you gotta know that you can never really know whats gonna happen with these techniques, because your basically sapping out free adwords credit and advertiseing from google, which means the support team can terminate your account at any time. I dont know why this works or why google isnt doing anything about this yet (or at least this is what we think), becasue basically all google would have to do would be disable the $50 promo link or immidiate freeze all fishy accounts (I dont beleive they cant track this somehow).
Ive had accounts go well over the $50 bonus. Not to thousands of dollars, but to like $150-200 over, and all I saw after that was when I relogged into the account, there was a red highlighted message saying processing the payment from the credit card failed. Of course, after that, I just left the account to its destiny and never logged back in again.
I suspected that that would happen so I didnt enter my own info into the cc form when I signed up. It was just common sense for me. Remember, this is blackhat, quite blackhat. Even just signing up to more then 1 activated account and just useing the $50 credits n no more is against their TOS, since its clearly stated that theres only 1 promo $50 sign-up credit allowed per person. So I suggest always entering in non-personal info.
The real risk of this whole business is hanging over the vcc sellers, who despite the fact of being able to earn like $500-1000 a day selling their vccs (and yeah thats nice money: they sell like 100-200 daily at $4-5 a piece. Not bad...), can get in real trouble once google finds out whats happening and tracks them down. Although I asked one of the vcc sellers about this and he told me his lawyer said the worst thing that could happen to him is him getting his bank account terminated.

So you cant really know what google knows or will do or not. You can just take the risk, put high hopes in your proxies and enjoy this method while it lasts.

Yeah, with prepay you need to pay $10 from your credit or debit card.