I like the idea of a thread about hidden features. Hopefully it will be a long one, and a place where everyone can learn something.
Here is something simple: AC key shortcuts. It never ceases to surprise me that people don't know about these and use them regularly (F-9; ctrl-s; etc.). They add up to significant time savings.
In AC, go to help...contents... and type "shortcut keys" for the full list.
