[X4]

Btw. here's a link: http://www.duetapp.com/

Personally I wouldn't ever use a SaaS for my core business! With Duetapp or other opensource project for example, I am able to modify the source it. (opensource!=free)

Regarding duetapp, I think commerce and organization should be seperated. But no other invoicing app does that atm. anyway. However I feel that this is the last bit required to make it almost perfect. Basically I would create a clean and modular and payment gateway, so that I can be used by any other app too. Write a little duetapp plugin and voila. Much better than integrating every single payment method manually into system A, system B etc.