I'm surprised and worried by the fact that the question about Collatz conjecture stays opened.
Let me explain myself. There were many cases, when different people couldn't agree whether some particular question is ontopic/subjective/... and should be closed — and it's ok, there always is some «gray area». But in this particular case even supporters of the question say (to quote TonyK): «You are right -- it's not really a question. But to delete it because of that?» and «I am frankly surprised that a mathematician would object to this post simply because it violates the posting rules. Like you're a zombie or something.».
And this (especially when the corresponding comment is highly-upvoted) really worries me. Do we still agree that math.SE shouldn't become another Reddit but stay a place for asking and answering mathematical questions?..
Upd. I mean, there can be exceptions of rules, of course. But in each such case there should be some important reason for this. «Every rule can be broken, but no rule may be ignored.»