Ask HN: Comepetitive Research for the App Store?

What tools/techniques do I have available to me to put together sales projections for an as-yet-unreleased iPhone app?

For any given app I can look at the ranking history, the price, the number of reviews, etc., but it's difficult to extrapolate that into something I can put into an investor presentation.

In certain categories (esp gaming) there are groups of app developers who have gotten together to share sales info, but those are very few data points (and not in the category in which I'll be competing).

What data are you using to come up with sales projections?