GregV: I regularly bike on the footpath on one particular section of road. The roadway is quite narrow, and prone to sun-strike on the way home. On the other hand, the footpath is quite a long way out from the fenceline, so I have good visibility of cars exiting their driveways. Hopefully any police officer pulling me over will agree with me :)
I think it depends on how fast you are going. As long as you aren't riding faster than someone walking, so there is plenty of time to see cars exiting driveways, I don't really have a problem with people riding on footpaths. It is the cyclists that speed on footpaths that are the problem. Not sure if there is a speed limit for people traveling on footpaths.