Good question! It's actually very simple. Once the forum hits 2,000 posts I will declare the top 3 MVP posters and issue the Amazon gift certificate.
An MVP poster will be on that offers informative and helpful posts on a consistent basis.
I've left the definition somewhat vague as I've seen the results of a rigid criteria with contests like this. If I give the award to the users with the most posts I'll end up with a lot of short and uninformative posts. The point it to build the community without impacting quality and a natural growth.
The winners will be chosen by me and it is purely based on the value that has been created by the poster to the community.
Thanks again!