I'm afraid there are PCI implications of doing things that way. You would need an encrypted database, and would probably also have to have regular audits. As such, so far, all nBill gateways avoid storing card information in your database. I understand OSDCS have written a Paypal Pro gateway, which takes card payments directly and processes them server-to-server with Paypal (so there is no need to store the details, but also no need for the user to leave your site). I have no plans to write a manual gateway that stores card details in the database though (although there is nothing stopping anyone else from writing one - just make sure you are PCI compliant, otherwise your merchant account could be suspended).