When Chris Cheung and Thomas Heermann, two middle managers at the software company Autodesk, first showed off their new iPhone drawing app, they got some skeptical looks. Why would anyone want to doodle on that tiny screen? And what could a $2.99 app matter to a company with around $2 billion in annual revenue?

Two years later, Autodesk's SketchBook apps for phones and the iPad are best-sellers that have been downloaded seven million times. It doesn't add up to a huge amount of revenue: perhaps $15 million. But there's more than money to this innovation story. With its first consumer hit, Autodesk now has more customers than it did in all its previous 29 years combined.