I belong to a forum which has a long row of buttons for use: like, agree, disagree, informative/useful, craftsmanship/clever, thanks, funny, friendly/sympathetic, unsure of meaning. The ratings are displayed under a post, like in the example above and if you hover over somebody's username you see how many positive/neutral/negative ratings they've had. Pretty much everyone finds them easy to use (and this forum has an older and less tech savvy membership than FT).
The rating buttons aren't obtrusive and they work very well. It means that rather than 29 sypathetic posts about my brother being rushed to hospital a few months ago I got 29 friendly/sympathetic votes - far less clutter.
I don't see them being used to reward wrong information, or as a popularity thing - it's much more subtle than just positive/negative ratings which, IMO, are a destructive influence. Disagrees do occasionally prompt toys being thrown out of prams, but generally by people who are prone to that kind of thing.
That said, the forum in question is rather less stormy than FT - sex, religion and politics are banned subjects. I'm certainly not sure that an 'unsure of meaning' button is appropriate for a forum with so many people for whom English is a second language.
I would see the advantages for FT of implementing this system as being:
*Less post padding, since it would take away an excuse for doing so
*Fewer posts with no useful content
*Less cluttered threads with information easier to find
*More obvious how useful somebody's contributions are/what they contribute
Disadvantages would potentially be:
*Use of negative ratings as a form of bullying/rudeness
*Ratings causing an argument
*Risk of posts being erroneously described as useful
*More double posts - at the moment I have a bit of a problem because a TR type thread of mine has accumulated numerous likes but no replies so it looks like I will have to double post in order to get the next installment up.