Great idea - few things:

- You could have problems with mastercard wanting to protect their trademark.

- Your homepage is pretty heavy on copy. The copy's a bit long on hyperbole, too. Maybe edit down a bit and add a banner pic/video. Webapp homepages are a bit of an art, but good ones are fairly formulaic, too. Lots of examples out there, smashing magazine is always worth a look for inspiration.

I didn't try your app (not really very useful for me), but I think if you fix your homepage, you could convert really well. It's a problem a lot of people could use help with.