I made -4 the lower limit a long time ago because there used to sometimes be a very unpleasant atmos of piling on when someone said something unpopular and the score would go down to -10. But I noticed that some people were starting to take advantage of the fact that this meant you could make an asshole remark at the cost of at most 5 karma points. Now there is no limit to the cost.
The reason you see -5 is that the code that changes the score is just Javascript that runs when you click on the up or down arrow. View source and you'll see.
(1 hour later) so has anyone managed to get the other message below 4? I can't vote on my own comment, obviously.
Actually, I have got more upvotes for other comments since then, so while my total 'should' be about 5345 if -4 were the limit it's actually 5335.
edit: dammit dammit dammit