Not sure what would qualify as enough, but if you are like me, chances are that you would at least hover over "Yelp Sort", when you see that it is the default sort, as compared other more easily understandable things, like Votes, date, Rating etc. And if you do hover over it, here's what you will see:

    Yelp Sort attempts to show reviews that help consumers make informed decisions. The order is determined by recency, user voting, and other review quality factors. This method is applied to all businesses, sponsors or not.

If you go to their FAQ, you will find another question that clearly addresses it:

  • Are reviews displayed in any particular order?
    Users can decide for themselves how best to order reviews by  clicking one of the links just above the reviews (e.g., date, rating,  voting, etc.). Yelp's default sort order takes a number of factors into  account and reflects our own attempt to present reviews in a meaningful  order.  For example, we'll favor reviews from your friends and the users  you follow. The sort algorithm does not take into account whether the business is an advertiser or not.

In my opinion, this is just enough information and at just the right places. Most users won't even bother about the sorting algorithm, and will make their decision based on top 3-4 reviews + overall rating. Those of us, who do care about how exactly are the reviews ordered, would perhaps look for it (in FAQs or in the hover-over tool tip). And even these guys would not perhaps want to see this information every time they make a search.

See question on Quora