Think I recently heard that if more than 30% of your body mass was made up of fat then that was considered to be bad. Can't remember what sort of bad specifically, because these terms are unhelpful, just generally bad.

Actually, here (http://www.healthchecksystems.com/bodyfat.htm) is a link about it. There are a number of ways of measuring your body fat percentage, of which the bod pod (http://www.usnews.com/usnews/nycu/health/hescale.htm) (see the bottom) sounds the most reliable, convenient and fun.