On Wednesday, Digg finally launched its iPhone app , and within about 24 hours, it’s shot to the top of the app store’s “news” category in many countries around the world, including the US (where Mashable’s app [iTunes link] currently sits at #16). Now that the app’s live [ iTunes link ], there are a few notable features to mention that we didn’t know about when we obtained some exclusive screenshots earlier in the week. In addition to the ability to browse, search, and Digg/bury stories, there’s also options to save stories for later viewing, an in-app browser, and a “preview” feature for each story