Thought of a new business model for the Mac App Store: As there are no in-app purchases (not yet?), why not write an app with a basic functionality and sell it for a moderate price. Then over time add more and more features and raise the price with each new feature. Users buying early will benefit from the relatively low initial price and support the developer at an early stage, while users buying later will pay more but will benefit from the already more extensive feature set. Will give this another thought.