I would think that if three people voted my post up and three voted it down then I would see no reputation change, but in fact that is not the case. Why?
The proposal to increase the weight of downvotes was extensively debated on meta.SO: Should the weight of downvotes be increased?
It was declined by Atwood with the formulation
Downvotes were always essentially cosmetic, with an extremely minor effect on reputation. Despite this, received downvotes are taken quite seriously by users. Almost too seriously. If we raise them to -5 they are no longer cosmetic but can be wielded as cudgels on other users. This was never the intent of a downvote, so we would be twisting it into something ugly. Users are far, far more attached to their reputation scores than I ever could have predicted, and I believe more than doubling the weight of a downvote will cause a lot of new, additional angst in the community over the occasional received downvote -- to the point that only users who want to hurt other users will cast them. Downvotes go from being cosmetic and psychological to weapons of war.
I think Atwood is right here. Witness the multiple angry threads created by downvoted users here on meta... then imagine what would happen if downvotes hurt 5 times more.