I think two scenarios would usefull. One only letting you signup once and another with the posibilty to renew the signup sveral times. I have seen such szenarios with some portals offering access with costs for "normal" users like prof´s or teachers, but a free option for studends or pupils.

May you can solve this by giving the additional option once (true/false) to every "plan". Then it there would be more possibilities for subscription plans, not only a "free" one.

Yes, that´s what i was thinking of, a "one time mark". The portals I was talking of review all registrations and for the free options e.g as student you have to send a fax with your student ID to the provider. If this does not happen, they lock the acount a few days later.

That's a horribly good point. I hadn't considered cheaters.... I don't want to make it easy to keep accessing the content for free but I do want to offer a "try before you buy" option because I believe in my product.

Perhaps a unique ID will be their e-mail address or physical address. Does anyone else have an idea that will help keep demo access from being exploited?

Scott, will a free plan option come with one of the future releases? That would be great!