True, but I'm not so much thinking about small bumps as having to hold it relatively still and pointing at your face. With a laptop it's easy, the thing has a large base and even if it's on your physical lap it's not going to move that much, and it's oriented so the camera points at you when at rest. A tablet device on the other hand, well, try it with a small mirror, how long do you want to hold it like that? How jarring would it be to the other end when it shakes (minor steady-cam business aside)?

I could be wrong of course, maybe people would get the hang of it quickly, but it seems like one of those potential features that people look at with their rose colored glasses (like full OSX on a tablet, imo), without really thinking about what it would be like in practice.