I was looking at my user account settings today and wondered what this rating really signifies?

I guess at least mine don't mean too much, as I have earned a great part of them for either posting screenshots myself or for commenting on other peoples' screenshots .

I'd say, that it's more or less like Facebook's "Like" button, at least that's how I see it being used.

I click the up-arrow when someone is particularly helpful or the information in their post is good advice. Mostly I reserve it for technical/flightsim information rather than just "like".