Apple announced this week that developers have created more than 100,000 apps for its App Store for iPhone and iPod touch customers in 77 countries. Users have downloaded two billion apps to date.

Some music apps are instant hits. “With 10,000 downloads a day, worldwide customer response to our I Am T-Pain App has exceeded our wildest expectations," said Jeff Smith, CEO of Smule. “The App Store has given us a unique opportunity to create and grow a very successful business".

But while exact numbers are hard to come by, it's also clear that many music iPhone apps - even free ones - are downloaded far less often. Even as iLike, MobBase and others make it easier and more affordable for every artist to create an app, its becoming increasingly important that they consider how to make their app stand out, as well as, if fan demand exists before joining 100,000 others in the App Store.