"Hidden features" is a series of poll "questions", without being answerable questions in the sense that Super User is a Q&A site, that started on SO and is now largely discouraged. Due to popularity, older "hidden features" questions are kept, even though they make poor questions, though I believe they should probably be closed and locked to avoid copycatscopycats.
Also see the comment on your question:
poll-style questions like this are discouraged; they are better suited to discussion forums. Super User is designed for more concrete questions. a question like superuser.com/questions/149055/… is a bit more palatable because it's restricted to the uses of a single program. as @hotei's answer points out, none of your own examples are particularly "hidden features" of Ubuntu.
But I hope everyone changes their minds, because I just posted 50 "hidden features" questions on Super User:
- Hidden features of Edubuntu 10.04 LTS
- Hidden features of Windows for Workgroups 3.11
- Hidden features of Vim
- Hidden features of Emacs
- Hidden features of Geany
- Hidden features of Google Chrome
- Hidden features of Opera
- Hidden features of Firefox
- Hidden features of Mosaic
- Hidden features of XChat
- Hidden features of Screen
- Hidden features of Less
- Hidden features of Sed
- Hidden features of Ed
- Hidden features of the Magnetic Needle
- Hidden features of Butterflys
- Hidden features of parsing HTML with regex
- Hidden features of insanity
- Hidden features of pharmacology drug abuse
- Hidden features of god, where does it end?
