I thought of that, but 1) if you're invested enough to go do that, you're likely to already notice posters you 'like', 2) even high-karma people can say stupid

I thought of that, but 1) if you're invested enough to go do that, you're likely to already notice posters you 'like', 2) even high-karma people can say stupid things and vice-versa, and 3) there could be a 'percentile' system where the top x% get some kind of marking, or even just 'in the top x% of karma).