1. I am 95% sure that Google will process your CC and send money to the developer (less their commission), so you should feel pretty safe. This is just a guess, I haven't tried buying anything yet. Or they put it on your phone bill?
2. Once you bought it, it's yours, for as long as you're on the same account (and maybe same device) - once you paid for it, you can re-download it at no charge. Or so Google says. When I uninstalled one of the (free) applications through market - it showed a message saying, that even though I'm uninstalling it now, I can re-install it later at no charge.
LEM.