I have been using this product with Leopard Happily
After you send an invoice and they pay just change the pulldown menu to receipt make a note on the bottom Paid In Full and the check number and one click on the button it's emailed to you and your client. I really am very happy with this product. It has a nice search feature too. Just click on a customer and click the type of document you wanna do and it walks you through step by step.
You can access this anywhere you have an internet connection. No need to install any software as it works right in the browser. You can do it right from your laptop on location if you want, but most of the time i tell them I will email it to them. I have emailed the tech support and he is very helpful and bends over backwards to help.