I change my brush after I can't be bothered to pluck all the pubes off it.
but seriously, by the time the bristles show signs of wear I go and get a new brush, it usually takes a little over a couple of months
although sometimes I just wait till my girlfriend has to change hers to so that we buy both brushes at the same time
unless it's an emergency, then I'll take a brush from the "visitor pack", since every so often we have parties and get togethers at our place, we like to have spare brushes in case anyone passes out or decides to stay over
as far as razors, those usually get changed every two weeks or so depending on whether I'm growing a beard or not
I use my girlfriend's shaving cream for her legs cuz I have very sensitive skin
shouldn't this be renamed the personal hygiene thread or something?