Some additions:
It seems - haven't tested extensively, simply tried - that the damage from skills like splitting arrows, poison arrows etc. does not stack with your normal bow damage, but rather replaces it. This means that for a warrior, with the largest damage bonus of all classes, these skills are quite useless; relying on bow damage alone + bow skill seems much more effective, pluss Poison Weapon for extreme effect. Long sight range is a must of course as you can only concentrate on one enemy at a time.
In my hardcore games (Hard difficulty + no reloads) I found skilling the warrior as an archer a bit hard as far as survivability goes. Agility doesn't protect you enough in melee (too many enemies that can one-shot you and will do so at some point, no matter how high your defense is), so heavy Con would probably be better in the long run.
A note about looting, I haven't read tips about it, but I remember reading a long time ago that the way you killed an enemy had an influence on loot drops, and this seeems significantly true to me. Melee tends to net the worst results by far, ranged combat does better, and magic best of all; so adding archery to your warrior might improve your survivability a lot. Of course, this is far more vital in a no reload game than usually.
