I used to have an extremely popular question on StackOverflow:
Interesting uses of sun.misc.Unsafe.
It was an extremely popular post and one of the go to places on the internet to learn more about the sun.misc.Unsafe class and how it is used inside most modern libraries. It had been viewed over 40,000 times. Most discussions on the web related to the Unsafe class would refer to this post.
However, the mods at StackOverflow deemed it was not 'question worthy' enough. First they locked it to prevent more answers and have now completely deleted it from StackOverflow. This was after me trying to change the title to suit the mods' requirements and countless comments on the post to not remove it.
Since it has been marked as deleted, the page will no longer appear in any search results. Only direct links to it can get to it. Here is a link to it.
StackOverflow removed a genuinely good page which had a ton of useful information that was not available anywhere. They could have even just kept it as 'locked' and not deleted it and atleast that resource would have been available. Now it is just gone.
Update: Apparently direct link is only visible to logged in StackOverflow users above a certain reputation. To the rest of the world, it is fully deleted.
Update 2: Thanks to the Hacker News community, the post has now been reopened!