I can safely say that I agree completely. I rarely chuck out any makeup but it can in fact be a breeding ground for nasty bacteria as I discovered first hand last week when my bacterial conjunctivitis came back - yuck!! The Doctor told me to ditch all my make-up, wash towels and bedding and be extra careful. It had been coming back a few times and I have a sneaky suspicion that my eyeliner was to blame.
So it is well worth replacing eye makeup and washing brushes (Mac do a good cleaner) and fingers crossed all hopefully all you'll be seeing in the mirror is a lovely face with no nasty surprises!