Very useful feature. It would be much more useful, if it searched the typed in phrase anywhere in the action names and not just at the start of them. So when I type in "usage" I want to see "Find usages".
Also support for camlehumps or whatever it is called would be nice "FU" would find "Find Usages" "CS" would find "Change Signature" and so on.
If you would initially show the list of most common actions in a given context, I could dump my NaviActionPad plugin :). But seriously, this could be quite useful. IDEA would track the actions I execute most often when the cursor is on a method name or on a directory and show this list the next time I press CTRLShiftA on a similar element.