John,
Sorry, I should have clarified what I meant about selling metrics, as that does sound kind of awful shady marketing ploy to collect identity data, which I did not mean to imply. I was thinking something like a Comscore, or Nielsen ratings kind of information. IE since you are collecting search stats, you could easily have the information on "popular search terms over the last 7 days" which would contain information from all the major search engines that lead to sites using woopra, etc. Yahoo, MSN, and Google all collect this data, but for their own service. You would be seeing it across all services.
I think if you are going to offer the full boat of services, that maybe it should be based upon traffic. A site like mine, is a personal blog, and gets very little traffic. My site's overall impact on the service as far as collection goes is minimal, compared to a large ecommerce site with tons of visitors.
So, I could see you setting site classifications, so that smaller sites can still use the service, and the larger volume sites pay into using the service to offset what resources they use.
Statcounter.com used action log history as a differential. Smaller sites with less traffic took longer to fill the log span, while larger sites would fill it quicker, so they sold larger log spans for the higher volume sites. Everyone has the same bucket, but more active sites fill the bucket quicker, so they may want to buy a bigger bucket to contain stats to trend off of.
You had mentioned in a previous post about a 90 day stat retention window. I could see for sites interested in long term marketing, as longer time spans being something they would want to spend money on.
PS - not a marketing guy...just a techie guy... I have no idea what I am talking about here :)
