Nick.

Thanks for that one. It never entered my head to dream that up on my own.

I have my doubts that the sand or water device would work unless you used a pulley and pan head with an extremely low friction rating. I can see anything turning that slowly having big problems with 'slip-and-stick', IE, jerky motion. Come to think of it, that could be a major obstacle with any device trying to move a heavy camera that slowly. You'd have a lot of starting friction in the pan head to overcome. Any driving device you connected would tend to repeatedly build up tension before overcoming the starting friction, resulting in tiny bursts of movement rather than a smooth, flowing pan. At a normal panning speed this isn't a problem, since once you overcome the starting friction, the 'moving' friction comes in to play. At those extremely slow speeds, you would really never get the head into 'moving' friction. To overcome this, you would need some sort of zero-friction pan head, like a block of wood floating in water.

Mounting the camera on a large lazy susan-like disc and connecting a clock motor gearbox to the outside edge might work. Sounds like a fun project for next weekend!

I don't think pulley stiction should be much of an issue, you can easily find one with low mass and the tension to pull the arm can be quite high. Stiction of the head is definitely an issue, but I think the issue applies as well to the motorized drive - both solutions need to apply sufficient force to move the head at a constant rate and a decent head is assumed. It's possible to choose a weight sufficient to do the job with the dropping weight method.

I really like the water clock approach which could be highly adjustable. The motorized solution would of course be easier to use, a stepper motor and timer control is the usual approach in telescope tracking solutions. There is also a device called the "barn door drive" which is a poor man's astrophotography solution. It uses two pieces of wood hinged at one end and a threaded rod turned at a constant rate (e.g. quarter turn every 15 min) to adjust separation of the free ends (with hinge axis pointing at North Star).

Check out my solution... very inexpensive too: http://www.youtube.com/watch?v=Ni89TBOTCUA