Forbes's account of Dropbox CEO Drew Houston walking away from a nine-figure deal in 2009 from Apple shows the quintessential Steve Jobs, who dubbed the company's cloud storage service "a feature, not a product."  And, what's a startup story without visits from Y Combinator's Paul Graham and With iCloud rolling out to millions of users and everyone from Microsoft to Amazon jumping into the cloud storage game, even Dropbox's recent $4 billion valuation — and $250 million in funding — won't guarantee success.