I try to keep to the same system as you do, nwr. Exceptional posts which make their point with clarity and intelligence are worthy of a cheer and if they include humour, so much the better (yes, Dr A, I mean you and your marsupials!).
It doesn't matter to me whether the post agrees or disagrees with my position, if it's well written it deserves a cheer.
I reserve my jeers for posts which include dishonesty, incoherence, ad hominems and totally illogical thoughts. It is a way of saying that the post doesn't make any decent argument, rather that a way of showing disagreement with the argumet.
Some, however, use the jeer button indiscriminately on those who they consider to be on the opposing side, regardless of the quality of the post. Granted, they are in a minority, but they work hard and it isn't uncommon to have a long sequence of posts jeered by one person who just doesn't agree with the position.
I don't know how easy it would be to implement, but I would suggest a wee dropdown menu for the cheer/jeer button where you could click on a reason for your choice, otherwise your choice doesn't register. It's only a 2 click process, rather than a one click process and might even go some way to helping us improve what we post by giving us a little bit of feedback on them. I for one would appreciate knowing what someone found good or bad about my posts, whether they were confused, or contained factual errors, or were well-argued or very clear.