What are the biggest App Store Optimization drivers for you?

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We've been looking closely at App Store Optimization: the study of driving organic (read: non-paid) app downloads. Think of it as SEO for apps.

As we focus on growing our apps and talk to developers of other apps, we've come up with three drivers of organic app downloads:

1. Rankings: Where your app ranks in the Top [Free|Paid] [Category] Apps charts. Also, where your app ranks for particular search queries (e.g. if you're building a sudoku app, you care about where your app ranks for "sudoku" search queries).

2. Sharing: How often your current users share your app with their friends (via SMS, email, FB, Twitter, etc).

3. Press: How often press (app reviewers, bloggers, newspapers, TV, radio, etc) talks about your app.

I put my thoughts down in more detail on our mobile developer site, MobileDevHQ. Also, we're thinking about creating some tools for developers to help manage their App Store Optimization process. If you're interested in learning more about those (and helping us shape the direction of those tools), just enter your email address at this form.

What are the main organic app download drivers for you? How do you measure these things? How do they compare to your paid download initiatives?