I lease a number of aircraft to a flying club and I charge for take off to landing.
The taxi time is not an issue to me as I lease the aircraft "dry" but the reason that I charge Take off to landing is one of flight safety after all if a pilot is not paying for taxi time there is no reason to rush the checks or take off with a cold engine.
Only time will tell if this is the correct policy but if the engines reach overhaul with the cylinders only being removed once for a look at the top end I will be happy.
I won't use a hobbs or the tacho to record times but if I suspect that a pilot is cooking the books the fuel uplift is sure to catch him out, I have also considered fitting GPS loggers to the aircraft to automate the invoicing but the drive to do this is to cut down on administration costs rather than squeeze the customers for more money.