This is specifically about the apparent frequency of the appearance of high-vote answers in "related links" that don't seem to be related. The examples below will use SO but this applies anywhere.
For the most part, the related links are useful. However, there are certain questions that I constantly see in the related links, but that aren't really related. In particular, the ever-popular Why is it faster to process a sorted array than an unsorted array? is almost always in that list, e.g. it's in the related list for Why am I able to have a public member in a non-public class?:
Of course, the sorted vs. unsorted array question is not related to every single question about Java, ever. However, StackOverflow seems to think it is, and so it's essentially just reducing the number of slots for truly related questions.
Another similar question is The Definitive C++ Book Guide and List, which pops up on the majority of C++ questions regardless of their content.
Point: I think that something may be off with the way that the vote count affects the "related-ness" of a question. Is there something that can be done to clean this up a little? Perhaps a hard upper limit on the amount that vote count contributes to the relatedness (high enough that it does not interfere with the current otherwise-good calculation, but just low enough to keep monster questions from "tainting" the lists)?
This is not intended as a comment on the general quality of "related" questions; I think it's actually quite good (and there are other discussions about that). I'm specifically referring to certain questions with high vote counts that constantly appear. It's not a major issue, it's also easy enough to ignore; but it does seem like a flaw of some sort (perhaps this post should be tagged bug instead of discussion?)
Other examples of good related lists "contaminated" with an unrelated high scoring question:
On Meta: Stack Overflow is getting a place of its own (238) and https://meta.stackexchange.com/questions/221594/2014-so-moderator-election-qa-questionnaire?rq=1 (295) on the side of this very question.
The "sorted vs. unsorted array" question, of course, is the biggest offender, along with the "c++ book list". In general, if you pick 10 random questions (especially from c++ or java) you can probably find one of these topics in at least 7 or 8 of them.
As time goes on, the issue grows:
It's starting to get a bit out of hand (just over one year after I originally posted this). For example, on SO:
60% of the "Related" list is unrelated high-voted content. That is not the intent of this list, at least as long as it's titled "Related" instead of "Popular". As popular content becomes disproportionately more popular over time, the issue will only continue to worsen. It is beginning to affect the quality of the list.
Now, I do notice that the two main examples above (unsorted arrays, and C++ book list) in particular don't seem to appear in many related lists any more, so clearly something was changed -- but it seems like the change was just to explicitly exclude those specific questions from related lists (?) because the other examples besides those remain unchanged, and the behavior still exists in general.