Limitation of duplication / reputation spread
Ideally you should not be able to constantly negative (or positive possibly) the same member repeatedly) , I'd guess this was why IPS switched off giving negative rep totally as people were searching for posts by certain people and neg'ing them all.
I think a small addition (from memory VB actually does this anyway) , you should not be able to rep the same person again within either x hours and / or before giving rep to others. Let me go into a bit more detail with this one.
User "Joe" gives "Bob" a neg rep for something. "Joe" now cannot give another of "Bobs" posts a neg rep till either x hours have passed and / or he (Joe) has given reputation to others.
Appreciation (Perhaps that's not the best word for it)
Rather than a massive query in a members user CP to see who gave what, I think for each post you should be able to click on the rep number and see who gave you points just for that post.
Going into more detail on this: Should work the same way as the public poll pop-up ideally. Perhaps an ACP option to only show positive points or both, and each member should (maybe) have an option to turn this on and off (ie: keep my reputation private from other members)
EDIT... And keeping in with this topic, please consider (everyone who reads it) give this post a + or - (I don't mind) if you like or dislike my ideas




