Here are two others.

http://www.webbicycle.com/about.php

http://oxfordchainless.com/

Some claim that power is more direct with a chain since there are no angles as in a shaft drive. But, if you don't keep your chain clean you lose power, and since the shaft drive is sealed dirt and grit are not big factors. The shaft and casing weigh 3-4 pounds, an extra load.
If you need to repair your shaft bike beyond the normal and you are not mechanically oriented, you might have a problem. Also changing rear flats could prove to be a little difficult.
However, a shaft driven bike with an internal hub would be a very low maintenance bicycle.

Some discussions here:

http://www.bikeforums.net/showthread...t=shaft+driven

http://www.metafilter.com/mefi/27053