We can't say we know all that many people who routinely digest articles posted through Medium's social publishing platform. However, the readership is bound to go up now that the service has released an iPhone app. The mobile client is more of a story curation tool than anything else. It automatically fetches stories from both your Twitter friends and any collections you follow, optimizing the reading interface beyond what you'd normally get in your web browser. You won't want to plan on writing any diatribes, though, since the iOS app has no editing tools -- you'll have to retreat to a PC when inspiration strikes. If you don't mind that limitation, Medium's client is ready and waiting in the App Store.