My wife discovered a quick and nasty diagnostic procedure for a bad ignition switch. Her Accord's symptoms were classic: intermittent stall unrelated to road speed or RPM, occasional non-start, you get the picture. Her insight (no pun intended):

Turn the key to the start position. When the starter starts to turn, let go of the key, allowing it to snap back to the run position. If the instrument warning lights go out, the switch is bad.

This seems to work on a couple of different cars, one with a known bad switch and one on the way downhill. And, by the way, the All-Knowing Honda Dealer Computer System insists that the ignition switch recall has been performed on both.

 

Yeah, that probably gets the key to rotate further 'back'.

Another test is wiggling the key or holding it just barely into the spring-loaded part of it's rotation. Not far enough for the starter to keep running.