I always keep around some 100mg tabs for emergencies, that is, if I can't get to sleep at all but have to function the next day. 50mg knocks me out within an hour, but as I said, I only dose on rare occasions, maybe twice a month or so, depending on circumstances.
I'd strongly suggest not taking doxepin daily, tolerance builds quickly and the side effects (dry mouth, grogginess in the mornings) become more pronounced, at least that's what I've heard from people hooked on the stuff (yes, it is addictive).
Withdrawal doesn't seem to be too bad though, a bit of shaking and trouble sleeping for a couple of days, but all of this is second-hand information as I've never been addicted to this substance, so please correct me if I'm mistaken.
Good to know that lower doses work just as well for sleeping purposes, always great to learn something new (and make my stash last longer

).