A Dutch startup has launched a service that studies data from social networks to quickly identify online service outages -- sometimes, it says, before the service providers know about the outages themselves. Downdetector.com, which rolled out in the U.S. last month, sees itself as "the weatherman for the digital world," by detecting outages and interruptions on cellphone networks, banking services, social networks like Facebook and Twitter, and business services such as Salesforce.com.