Roughly 38 billion apps will be downloaded in 2011 alone. But only a fraction will be used with any frequency.

The vast majority of consumers with apps on their smartphones use less than 5 per week. 38% use two or fewer during the same time period. That includes apps that they purchased.

Not surprisingly, 18-29 year olds are the heaviest users of apps, especially social media apps. Usage declines rapidly with age.

The apps that are most engaging to consumers are not the type many companies create for marketing or brand building. Instead, consumers prefer game (birds and pigs anyone?), weather, social networking, map, search, and news apps. Facebook is currently the most popular app.

Why don’t consumers use the apps they download? It’s partly due to overload---people can only keep track of so many tools. Plus, the low cost of apps makes downloading, trying, and deleting them more attractive than trying to assess their usefulness in advance.

• Are we building apps in consumers’ favorite categories?
• Should we stop using the number of downloads as the ultimate measure of our apps’ success?
• Do our apps target 18-29 year olds? If not, do we have appropriate expectations for their usage?