Something that many developers do, or would like to do is implement some sort of mechanism to allow their users to share their apps using a social networking site like twitter. Typically the users will have to either enter their information, or need to authenticate through the twitter website, and being able to do this should greatly increase the rate at which people can tweet. I found a great article today on a technique for sending tweets that requires the user to do neither.
If you’d like to know more about custom URL schemes you can read about creating them here:
Launching Your Own Application Via A Custom URL Scheme
An introduction the iPhone’s built in custom URL schemes can be found here:
Apple URL Scheme Reference