Based on Pinch Media data covering 10% of all application downloads, it is estimated that some 610 million or about 30% of at least 2 billion App Store downloads so far have been of paid applications.
This translates to some $900 million in cumulative developer revenue since the App Store was launched.
Paid applications as a whole are used slightly more often and for slightly longer periods than free applications, potentially a reflection of application quality or a consequence of increased user attachment to items that they’ve paid for.