I don't believe that the majority of these shipped app device units are being used in a true computing capacity. In my day to day exposure, smart phones in particular don't tend to be used for much beyond the capabilities of earlier cell phones.
Especially among the younger crowd, who now seem to think that owning an iPhone 4 is the new minimum requirement for acceptance by their peers, the typical use seems to mostly comprise texting and music playback, with the occasional use of the camera for taking pictures of their friends while drunk. Facebook has definitely made significant inroads, but not too many people are using advanced features of Facebook or using more complex web applications from their smartphones. Some games are present, which are definitely more impressive than what previously existed as games on cell phones, but which mostly fill the same role: idle time wasters when on the go.
In my office environment, everyone has a smart phone. No one uses one as a primary email device, a primary web browsing device or a general office productivity device. The dominant use is scheduling, which requires syncronization with their computer-based scheduling, and email & web browsing while not in the office.
iPads have made some inroads as a computer replacement, with a few people using them as laptop-replacements for meeting notetaking and presentations, but still they're not being used as a primary productivity device.
I see these mobile devices, currently, as a supplement to personal computers which can be omni-present. Because they fit in a pocket and combine functionality with a required gadget (cell phones), more people are web browsing on the go or performing some tasks that previously may have required access to a computer. They still have syncing relationships to computers that are critical to many of their functions, and most functions still work better from a real computer. I doubt that any time soon you will see someone replacing their work PC with a smart phone, and the consumers that might replace a home PC with one probably didn't use that home PC very much.