The way the gigapan works, which might be a good way to follow, is to aim the camera to where you want it to start via the arrow buttons. This drives the built-in servos/motors to aim the camera. Then you hit next and aim the camera via the arrows to the last frame and store that. It then calculates the amount of photos needed and the overlap based on a previous setting.
I could image having a small display on the arduino with some buttons. You move the head on the slider and aim the camera using the arduino driving the motors and hit "start" then move the camera to the end position and hit "end". Then the arduino could figure out the tweening positions and move through them smoothly for a video shoot or with intervals and trigger the shutter for a time-lapse. You would probably want to add a speed setting or an delay setting between shots or maybe a "time to complete motion" to have it calculate the interval time.
To me this seems like a really simple solution that could be adapted for a lot of different rigs, cameras and end results.
The only other type of calculation that might be wanted is a ramp-in ramp-out where you could ease into the motion and out. Maybe that could just be an onscreen value you could change.
BTW there are lots of Pan/tilt units already worked out at ServoCity. http://www.servocity.com/html/pan_tilt_ ... ories.html
And for a camera trigger with intervalometer there is this that might come in handy. I have one but haven't had time to play with it yet.http://www.dpcav.com/xcart/product.php? ... 253&page=1
Both of these above use standard RC servos which means they will work fine with the arduino too.