10MM - over or underrated? It can be useful in variety of situations and over kill in others. So when is it over kill? Well - my 2 cents - in most (not all) home defense situations. With the 10mm's increased power/ penetrating capability - you might want to consider friendly targets beyond the reach of the bad guys. I.E. - children/ loved ones in their rooms if you are forced to defend your home.
So when is it effective? In my humble opinion - the 10mm makes an excellent hunting round. (One of Uncle Ted Nugent's all time favorite pistol cartridges.) From pig hunting to black bear - the 10mm is not a round to be trifled with. As a hunter who has recently caught the bug for pig hunting - this round is definitely on my list of calibers to own. Will I carry it for my EDC - probably not.
Check on the Military Arm Channel (MAC) go more in to depth on his personal likes and dislikes of the 10mm. Warning - all you .40 S&W fans - might cringe a little.