[inerte]

If you can't find where to draw the line now, you can put the cap later but don't charge the existing free users.

Example: I have a very old cellphone plan. It's not available for new carrier costumers. But the carrier never asked me to change to one of their new plans. I'm just using the old one.

So you can tweak the caps anytime you want. Start with free and very, very generous plan but also very, very expensive. Then take some statistics. If a lot of the free people are using 50% of their way into the expensive plan, create a middle-tier one, where you charge 60% of the price but it offers 50% of the features.

I know I haven't answered your question ;) Just wanted to say that you don't have to be perfect from the start.

[mchadwick]

That's extremely helpful. Thanks. Sometimes it's a bit daunting to be very pragmatic up front.