Will increased weight make me go downhill faster? I have had this question for a while. I want to know how I can get down a hill as fast as I can. So, I was wondering if increasing the weight of a bike increases the speed on downhill stretches, or will it just slow me down because of rolling resistance, drag or other factors?

I am talking long stretches here, and long, 10-30% hills. I have also checked the road surface, and there are no bends, and I can easily see if traffic comes along. It is very rarely used for traffic anyway.

Thanks

EDIT: I would also like to factor in things like rolling resistance in this question.
The main thing you have to consider at speed is drag:
The force F on you+bike (mass m) is:

F = ma = mg sin Q - F_d - F_rr

where a is your acceleration, g is the acceleration due to gravity and Q is the hill angle to the horizontal. F_d is the drag force which doesn't scale with mass. Try dropping a balloon and a (soccer) football of the same size and you'll see this in action. F_rr is the rolling resistance.

Drag dominates rolling resistance at any decent speed for a well-set-up bike: More detail than you probably want or a nice graph so you should be able to neglect rolling resistance.  

Weight will have a small effect on rolling resistance and (assuming it doesn't affect the cross-section) none on drag so it will make you accelerate faster but not by much.

You might want to experiment: start with some measured speeds with no extra load, then test the extra mass, and a dummy load of the same volume/shape/mounting made of polystyrene or cardboard.

The biggest effect you'll have is on the drag - so the first thing to try is a better tuck, not wearing flappy clothes, etc.

For really high speeds a fairing is the way to go - compare the hour record for a fully faired recumbant (~92km) with a UCI racing bike (~52km).  There are no stats I can find specifically for an upright with a fairing.