Over the last six years, Dropbox has emerged as one of Silicon Valley’s most promising startups on the strength of a simple idea—allowing Internet users to store such files as baby photos and Word (MSFT) documents in the cloud and to access them from any computer or mobile device. On Tuesday the company gathered journalists in its swank offices in San Francisco’s China Basin to offer an update on its progress: Dropbox has more than 200 million users and its customers save more than 1 billion files in Dropbox every day. “There are more files saved to Dropbox each day than Tweets on Twitter (TWTR),” said Drew Houston, Dropbox’s 30-year-old chief executive officer. Dropbox also unveiled its next target beyond everyday Internet users: businesses. Houston says users are already bringing the service into their companies.