This is a very neat and simple application. Here is what I think you can charge for. 1. As jkaykin mentioned, limit clips for free users and unlimit for pro.

This is a very neat and simple application. Here is what I think you can charge for. 1. As jkaykin mentioned, limit clips for free users and unlimit for pro. 2. Provided a clean organized layout for pro users which can make them efficient. 3. Allow signup via email. I personally went to signup and was turned off by the two choices. No matter how many times you tell me, you don't spam my facebook wall, I will never signup via those two services. That's just me, but I'm sure plenty of HNers have the same approach. May be that's where your money is. Don't block us. </sorry> 4. I suggest one-time like pinboard, and up-sell a simple annual plan that has some neat features. You probably don't want to do monthly because, every time users see the charges in their bank, they will subconsciously reevaluate whether they should keep paying or find an alternative. So, having an annual/one-time/quarterly plan will minimize that reevaluation moment. This is all assuming that your product is easily replaceable. Goodluck