This is one of the topics I always touch upon when talking to web entrepreneurs who've launched sites. I usually ask it in terms of scaling and how fast someone

This is one of the topics I always touch upon when talking to web entrepreneurs who've launched sites. I usually ask it in terms of scaling and how fast someone should worry about it. What people tell me is that they were either surprised by how fast their site grew or they've been disappointed by the slow uptake. In either case, the models they've created were pointless. So worry less about modeling and spend more time planning for the best (or worst) case when you have so much traffic coming in that you have to scale up. Modeling is useful IF you're paying for the traffic. If you're buying traffic and you have X amount of dollars to spend per month, then it's fairly easy to project numbers. I'm assuming most of us here are building community sites and are depending on either viral or SEO traffic so you're left to more guessing. Edit: I just looked at the Powerset modeling they released and looked at their actual numbers on alexa/compete and you can see they're absolutely nothing like they projected.