If someone truly agrees with a post...seems to me the thing to do would be to say so in a response post...and perhaps add strength to the argument being made. If someone truly disagree with a post...wouldn't it be better to say so in a response post and give some indication of why the disagreement exists?
You'd think so Frank - but I'm on a bunch of listservs for professional reasons and I hate "ME TOO" replies. I think voting up a response is a very efficient way of signifying agreement/appreciation.
Imagine the Caption the Cartoon thread if every thumbs up was replaced with a 'Oh that was a good one George'? If you're really tickled you reply but generally thumbs make it flow better.
Even in debate threads reiteration without additional information wastes everyone's time, in my opinion. Often in drawn out threads my eyes are drawn to the high thumbs up counts (and the high thumbs downs too) - so I find them helpful for catching up on high traffic threads.
What would be really cool was if I could limit the thumbing I see to the people I respect. Peer review, if you will.