IPN URL: Just need to confirm: it's not necessary to specify a Notification URL in my PayPal account that points to ASP, since you specify the handler in the form code sent to PayPal? (I've tested this pretty thoroughly for a web app of my own; when you use the 'notify' variable it's not even necessary to have IPN on.)
Confirmed that is the case. I state that mainly to make sure users have IPN enabled in there account.
Is it possible to have a default ad per location if another user has not purchased a package? So one of my ads will always show unless the ad position is sold to another user?
How the system works is you can add multiple ad's per location. If you have your ad assigned to that ad location and someone buys that ad's location. Both ads are in then in the rotation to be shown in that ad location.
I just don't understand revenue sharing. Well, I understand the concept, but not how you've implemented it in ASP. Care to supply an example and explain how it works in conjunction with ad sales?
Revenue sharing allows your forum members to place their own ads. In ASP you can they can create either banner ads or text link ads using the editor.
The admin of ASP controls what % of the time user's ads are shown and what ad locations show user revenue sharing.
Normally revenue sharing is used as an incentive the more someone posts the more their ad would be shown in their topics/posts.