I've never got around to doing it and one of the reasons (excuses) is that I haven't yet figured out a way to stop bad actors exploiting it by, e.g., mass downvoting URLs of competitors. I did think about some sort of moving average, or bias toward more recent votes, which would at least somewhat mitigate against transient actions of this kind, but it's harder to deal with a sustained attack like this.
That is still exploitable: if I know you like A, B, and C, (perhaps those are popular items), I could also upvote those items and then downvote another item D. I have an idea for countering this: keep track of history. So instead of just measuring ratings overlap ("of items you've both rated, 75% of items were rated the same"), you keep track of the performance of recommendations made from that user ("of Alice's items that we recommended to Bob, Bob upvoted them 25% of the time").
I haven't thought about this super deeply yet, but I think to beat that, you'd have to actually provide valuable data to the system in the first place.
I would think the first case would result in way better data (which is why (I think) last.fm recommendation system is so good), but the latter case seems to be the natural thing to do, humans love to judge shit without actually engaging with stuff.
That brings up a key point which I'm not sure is clear to users or not: voting on items specifically means "this is/is not a good recommendation for me". It's not a judgment on the goodness of the item in general. So if findka showed me e.g. an article on pottery that looked high quality, I'd probably still downvote it since I'm not into pottery.
I'm sort-of trying to solve this with a recommender system approach.[1] Search isn't my primary objective; I'm mainly focusing on the case where you want to be made aware of relevant information on an ongoing basis but you aren't necessarily looking for something specific.
But that involves building up a ratings database of lots of different URLs. If it becomes really popular, I'd like to experiment with search. It could start with a "normal" search algorithm but then adjust the results based on rating data. E.g. "the top result for this query is X, but people with similar rating data to you always down vote that link, so we'll move that result down".
I've heard people complain about how Google gives you personalized search results sometimes, but I'm not sure if the approach is actually bad. Perhaps it could work if it was focused on from the start instead of bolted on.
[1] https://findka.com