I haven't looked much at Slashdot lately, but they have certainly put a lot of work into designing a good system for moderating comments. You are right that they have some dimensionality, and a way to "fade" trolls by adjusting your settings so you only see highly rated comments.

Still, for me at least, I don't find their dimensionality very helpful. "funny" and "informative" are rather broad categories. If all the content on Slashdot could be simultaneously ranked on a scale of "value to startup entrepeneurs looking for seed funding" and "online video content"...that would be useful to me!

I don't have any particular ideas about what should be done, but limiting your choices to "up" and "down" seems so narrow. Maybe I should jsut be happy it works as well as it does!