Starting around $300, Cinetics' CineSkates are not cheap but this new device may provide exactly the kit you're looking for in terms of mobile dolly shots. Attach your iPhone, start it recording, and use the rig to smoothly move the camera as you shoot, creating perfect rotation and tracking shots.
TUAW got its hands on an early review unit to see how it worked. We can report it felt extremely solid. The wheels plus the arms provided a stable yet maneuverable platform. You could adjust the camera to nearly any height within the limits of the physical components. Whether the camera was oriented up above the wheels or down as in this shot, it was steady and maneuverable.
That strength derives from those flexible arms attached to the skate wheels. They were surprisingly rugged, offering a great balance between adjustability and strength. Once the camera was positioned, it stayed in that position -- exactly what you're looking for in a system like this.
The wheels felt exactly like skate wheels, with all the smoothness you'd expect. There were a few times in our tests, where we had to re-adjust their position as they did have a slight tendency to squeak if they weren't placed in the proper orientation.
As far as end-users go, CineSkates are going to be exactly what you need as a video hobbyist or they are not something that fits into your life. For those who can use them, and who can benefit from the kind of high-end dolly system it provides, we think you're going to love it. Yes, it's not cheap, but from what we can see in our tests, it's well made and a solid buy.