Orkut developers often wonder why one of their very popular apps doesn't appear as high up in the directory as they believe it should. "Well, it's not exactly magic but simple math, and we wanted to share with you how our algorithm works out the rankings, and explain the way we rank applications in the orkut directory," stated Google.
In short, the formula looks something like this:
Total Score = Base Score + Popularity Score
Base Score = Score (total installs) + Score (weekly installs, adjusted for weekly uninstalls) + Score (weekly renders in canvas and profile views)
Popularity Score = Score(weekly renders / total installs)