Okay, I have to weigh in on this one. Sorry this will be a bit long, but I've been there, done that with this one.
I used to be a volunteer in the eBay Answer Center, which was a forum where people who needed help could get quick answers from other eBay users any time of the day or night. Many hard-core eBayers staffed the Answer Center. I used to spend about three hours a night there for a couple of years helping eBay users do things right, avoid getting scammed, and teaching them how to do what they needed to do there, much like we have here.
eBay also had a search feature where people could search old threads for answers to commonly-asked questions, much like we have here.
Then someone decided they wanted to find a way to have the best answers float to the top of the search results -- as has been proposed here.
So they implemented a "was this answer helpful? Yes No" to the bottom of each post.
Each thread was limited to 10 answers, then it locked. The point was to answer the question, not engage in endless debate. There was also a Discussion forum on eBay where topics could be discussed at length. Generally if three posters gave the same advice, there was little need to discuss it further. If OP didn't give enough information, the first poster would request the missing information, and later posters would discuss and reach a conclusion. Sometimes firestorms erupted, as also happens here at times. But after 10 posts, the fight would end because the thread ended.
The voting boxes caused a rebellion among the volunteers. I was among them. We argued with eBay. We wrote letters. We proved the boxes were causing the most popular answers to float to the top, not the most correct answers. Example: OP writes, "My item just sold for $10 but I was hoping to get $50. Do I have to sell it?" Well, according to the eBay rules (and common decency) yes, you do have to sell it for $10. Was this answer helpful? Well, what do you think OP would vote in this case? So he votes down the correct answer. The next poster writes, "I wouldn't sell it for $10. Tell the winner your dog chewed it up, wait a few weeks, and relist it." Hey, OP thought that was great advice! So that answer got the Yes vote. The other insidious thing was that anyone could vote. People voted No on responders they didn't like, voted Yes repeatedly on answers they liked or from people they liked. You could have multiple ID's on eBay; I have eight myself. Each ID could vote. So the voting could be manipulated.
Responders created taglines urging people not to vote, or saying, "Vote yes if you think eBay sucks, Vote No if you have fleas" just to prove how pointless the voting was.
But the thing that really ticked off the volunteers (and in case anyone missed the parallel, we in the forum are also volunteers trying to help people out of the goodness of our hearts) was the idea of inviting people who didn't know how eBay worked to tell these hard-working volunteers that they were *not helpful.*
eBay lost their best Answer Center responders over that. It was insulting and dismissive to encourage the people we were taking our time to help to tell us we were not helpful. Yes, we were helpful. We just didn't always tell them what they wanted to hear. After months of dialogue and protest, eBay still wouldn't budge. They flat refused to remove the voting boxes. About 300 of their best responders left the Answer Center, most never to return.
I can see the same thing happening here if a voting system were introduced so the best posts could be identified. "best" is a matter of perspective. A newbie who comes here to say, "I just took a shop for this weekend but my sister has tickets to a concert and I want to go. Should I tell the scheduler I have the flu so I can do it another day?" doesn't want to hear, "You committed to do the shop. Do the shop." They want to hear, "Go to the show, you only live once. There will be other shops." Every shopper who ever flaked a shop will be voting Yes on that one. Is that what we want on the top of the search results?
Most questions here are somewhat unique; the ones that aren't can be stickied in the new shopper area. Keyword searches are imprecise at best. Trying to sort the most helpful posts that contain the word "bank shop" is not going to produce anything useful to the person who wants to know if you have to be a customer of the bank to do a bank shop.
Having a way of applauding a good post is fine. A thumbs up button is good. The "like" button works pretty well. But a thumbs down or a yes/no vote will introduce negativity and a sour note to the forum and will not produce anything useful for sorting search results because most threads die a natural death after a few days and new topics come up. We have enough rancor here without memorializing it with a vote count that won't do anything to improve search results. A lot of keywords come up in posts that will be completely irrelevant to the topic.
Maybe a button for "archive-worthy" at the thread level, not the post level, could be added. If a thread gets 20 votes for the archive, the thread gets preserved and included in search results. If it flames and dies because it was a unique question not likely to be of enduring interest ("did everyone see that Maritz will be doing maintenance tonight?"
it does not get preserved.
But please don't put up a voting situation where anyone is going to tell these experienced and knowledgeable volunteers that their advice was not helpful.
Time to build a bigger bridge.