If I want to start a new website, the first thing I do is check out the competition to see both what they are doing and how much traffic they are generating. I would normally use a site like google.com to find the competition, and then a site like compete.com to find their traffic stats.
Now if I want to develop a new iphone app, I can use the cruddy app store search and some third party sites to find the competition, but how do I find out how many people are using those apps? It seems the only way to judge popularity is through the number of ratings. Are there sites like compete and quantcast that can give me statistics about the number of unique users an app has each month or at least how many downloads?