Massive problem with that is they are never, or almost never ever cleared of glass, grit, shit from trees etc. Stuff from trees is cleared off the road into cycle lanes on my route. So if you have racer or any narrow tyres, you'll be punctured the whole time. My housemate used the footpath and got a puncture every 2nd week, and his tyres were in decent enough condition. Coming off a bike from a sudden puncture isn't as bad as being killed by a car obviously. well maintained well surfaced segregation is what we'd like but that isn't a reality. Also people in and off of buses is a major hazard for cyclists on the cycle lanes on footpaths. 

Also the curbs for going up and coming off those cycle lanes are too lippy sometimes, the person who had the job to sand down the concrete into a proper slope didn't finish it off.