Okay, these are so many questions combined into one.. I will focus mostly on Yelp-sorting algorithm, or rather, my understanding of their algorithm, as the actual algorithm is not publicly disclosed.
You do have an option of sorting by number of votes, but I like their algorithm better. They call it "Yelp Sort". Think of it what are the factors that you would factor in, when deciding which review to believe in:
- Reviews written by friends: You are more likely to believe your friends as compared to random strangers.
- Reviews written by trusted Yelpers: Whose review would you trust more: A Yelp Elite with 254 reviews or somebody whose only review is for the business that you are viewing.
- Recency: A business may have learned its lessons from negative Yelp reviews, and now the reviews are all 5* and 4*. Won't it make more sense to give more weight to recent reviews?
- Higher number of Votes: Of course, as you mentioned, votes may help in crowdsourcing the decision of deciding which reviews matter most.
From what I have observed, Yelp-Sort incorporates at least these four in ordering the reviews. I believe that the highest weight is for reviews by your Yelp friends, which makes sense! So, if one of your Yelp friend has reviewed a business, his/her review will likely be on the top. Recency also appears to be heavily weighed!
Yelp Competitors: Urbanspoon comes to my mind, but even they do it on "Relevance" however you may want to define it.
Finally, while I love both Yelp and Quora, but I am sure Quora can not be a good substitute for Yelp. Yes, you can expect to get answers to questions like the ones you included as examples, but if it's already noon, you are feeling like having Thai for Lunch, and you need to choose between the 12 Thai locations within 5 mile radius, it may not be a smart idea to post the question on Quora. If you are like me, you'd likely turn to Yelp in cases like these!