Just a bit more than a year after we first laid eyes on iPhone OS 3.0, Apple is back with the latest big revision of the OS that powers the iPhone, iPod touch and iPad. It's shipping this summer, and the developer preview will be out today. The biggest new feature is multitasking, which Apple says is going to be the "best" implementation in the smartphone space, though not the first. App switching is activated by double tapping the hom
