If your site needs an FAQ, you have failed [END]
twitter.com
twitter.com
For instance a forum about hardware might see the same questions pop up over and over again and can save on pollution and improve the quality of the answers by creating a FAQ, much more time can be spent on a single answer that way than it ever could be when answering the questions ad-hoc.
Even HN could probably benefit from a FAQ, there are plenty of things that pop up over and over again in 'Ask HN' threads.
And in tribute to the OP it is certainly possible to have a short but strong statement about a subject that you can qualify as a rant and that still comes in under 140 characters.
'Goto considered harmful' would be a nice candidate.
Maybe one of twitters saving graces is that it is actually quite hard to get a good flamewar going in 140 characters ;)