In reply to minus273degrees:
A big fuss was made about this a few years ago, in Trail magazine, IIRC.
I wouldn't recommend it, as the formulations of conditioners seem to change all the time, so you've no idea if the one you buy will work as a DWR, or just knacker your jacket... At least the products sold as DWR treatments are intended for that purpose, even if they don't always seem desperately effective...