My buddy Greg posted a really great presentation full of awesome iPhone app usage analytics over at the Pinch Media blog (go full screen for some of the graphs). The data comes from the Pinch Media analytics platform and is based on the first 30 million downloads.
A few highlights: 1) You need almost twice as many downloads as a free app to hit the top 25 list today (20k) as you did three months ago (11k). 2) Long term audiences are generally 1% of total downloads (the usage dropoff rates for both paid and unpaid apps are pretty astounding). 3) “Only a few (<5%) high-performing applications are suitable for advertising right now, and you don't know if you've got one until after launch."