Apple announced yesterday that there are now more than 100,000 applications available for iPhone and iPod touch - but how many of them are actually being downloaded?

Only about 20,000, according to analytics firm AppsFire. "We have found out that actually 20k apps are actually used (meaning installed and kept on people's iPhone)," says the company.

That means a long and lonely tail of more than 80,000 applications that aren't being downloaded. A cautionary tale for any developer who thinks releasing an iPhone app is a licence to print money.

In fact, even the thousandth most popular iPhone app has only been installed by 1.76% of iPhone owners according to AppsFire - although on Apple's own figures of 50 million iPhone and iPod touches, that would mean a not-bad-at-all 880,000 downloads.

"The App Store is not designed for the long tail but for hits," suggests AppsFire. "No matter how great the App Store is doing, the discovery process is poor and only best sellers are really making it. This is even more true when you realise that most apps are downloaded from the mobile version of iTunes."

That said, Apple has introduced its Genius for Apps tool to recommend apps to users based on their previous downloads, which could help shine a light on some of the neglected apps in the store's long tail.