I'm a terrible DM and can't remember where I read this rule...

[Sorrow The Man Bear]

Somwhere I clearly remember reading that a dose of poison can be applied to one melee weapon, or twenty units of ammunition. Am I insane? Or a little bit stupid? I'll readily admit to either.

 

[Rystil Arden]

I'm fairly sure it's one dose for one object, be it melee or ranged. As per the SRD:

One dose of poison smeared on a weapon or some other object affects just a single target. A poisoned weapon or object retains its venom until the weapon scores a hit or the object is touched (unless the poison is wiped off before a target comes in contact with it). Any poison smeared on an object or exposed to the elements in any way remains potent until it is touched or used.

 

[Dagger of Lath]

Somwhere I clearly remember reading that a dose of poison can be applied to one melee weapon, or twenty units of ammunition.

Maybe you're thinking the spell "align weapon"?