Social Media Active Users by Network summarizes the number of monthly active users for all major social media platforms.
eMarketer provides performance benchmarks for several marketing channels including Social Media.
comScore publishes an annual U.S. Mobile App Report which is available by request.
Many measures of Social Media marketing and usage are compiled by ClickZ.
Demographics of Key Social Networking Platforms was released by the Pew Research Center's Internet & American Life Project earlier this year.
Over 170 studies and reports are available on the Online Database of Social Media Research from SocialMediaGovernance.com. The list is sortable by publisher (or source).
Constant Contact offers several Research and survey reports on the use of social media by small businesses and non-profit organizations.
A nice collection of recent charts and statistics is available at: Global mobile statistics.
The App Revolution: How this Varies By Market is a useful guide to sources of information on the smartphone app software development market.
Here's an infographic summarizing findings about the Social / Local / Mobile market.
A selection of other survey results have been collected by Bazaarvoice at Social Commerce Statistics.
Appcelerator/IDC Quarterly Mobile Trends Reports (formerly: Mobile Developer Reports) are available but registration is required.
Figuring the costs of custom mobile business app development summarizes data from several sources.
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