Looks great and something every app developer could use (I've heard many horror stories of using mailto: links). However it might be hard to make money on this when others are giving this functionality away for free as part of a larger offering (like we do; see http://www.uservoice.com/iphone/ ).
Similarly, a product my company is working on, Recon API, has a freemium model for a different but similar suite of tools.