I see a bit of a risk by AdWords customers taking on credit from Google advertising. I mean if you take out credit from Google to place ads it seems Google has an incentive to max out your credit line ASAP by placing ads. I personally don't use credit cards and I don't think I would go this route to advertise my business either.
But the way people seem to love credit it's probably going to be a success. Also this is an opportunity for credit reporting agencies (e.g., Equifax, D&B,etc.) to expand their market by selling reports to Google to risk rank Google's ad customers who desire the Google credit card.