As for #1)In-app Referrals - I'm not so sure if this would be a business, but on the topic of apps, why not make a "Compete.com for apps", where you can track how many downloads a specific keyword can net you, or how many downloads another app has over time. of course, this type of data is only known by Apple, but you can run some heuristics for estimating it.<p>Also app-store optimization is something that's relatively unsaturated now. Perhaps some sort of tool that runs statistics and gives you correlations on what factors goes into an app ranking high for a keyword.