I recently hired for the first time in years and was astounded to find that the club was charging tacho time + 0.2 hours per flight. This was allegedly because the tacho under counted time during ground running (which it does of course, but, as has already been pointed out, ground time doesn't cost much). This seems to me to be a way of disguising the charges so that hourly rates look good when potential flyers compare clubs. It makes short hops very expensive.
I've always thought that charging on Hobbs time was the worst possible arrangement encouraging rushed checks - and possibly even taxiing with the electrics off...