Short-stroking seems to be fairly common, Glenn. Every course I've attended or given it has reared its ugly head. That's one of the reasons I preferred my Beretta 1201 for serious social shotgunning.
While this thread started off talking about slugs I like the turn it has taken. Many hard core shotgunners think the only shotgun you can trust your life with is the pump (insert brand). They all have fairly decent reasons for thier position. If you consider the Full Line of munitions availible for the shotgun: breaching, less-lethal, reduced recoil and launcher pumps do rule. Their versitility also makes them a top chioce for "tuners and gear heads"
If you are looking for a purely defensive shotgun for the average shooter or LEO/Mil the semi-auto shotgun has a lot of advantages. My first shotgun was a Remington 870. I purchased it after 6 years in the Army. I thought it it was great, but would on ocasion find myself wondering why my shotgun wouldn't fire. Why? Because I was so used to the manual of arms of the M-16. pull trigger, repeat. I soon picked up a 11-87 and found my groove.
Semi's are easier to train in todays semi auto world. Pumping is one less thing to try and do under stress or in positions such has prone were pumping can be a real pain. I well maintained semi shotgun with proper ammo will serve 95% of all defensive shooters needs.
Only when you get into some of the extreams that the military and some police encounter or special munitions being employed do you HAVE to HAVE a pump.