Here is an idea for a feature that I've used before on a site.

For a post, readers could select to vote "I agree" or "I disagree" with a post, and at the top of the post you have a small thumb up and a thumb down graphic, and next to it a count of how many people either agree with or disagree with that post, which if you clicked could pull up a screen showing up disagreed / agreed with that post.

I like the idea
which could be forum / topic optional

seen this on other software and is used well

I mentioned this in my long list of feature requests a while ago; I like it ...

Is that on individual posts, or on the topic in general?

Individual Posts... Lemme see if I can find an example for you (it'll require a PT as topic matter doesn't "fit" with threads support)