M.T. I guess when I wrote "I haven't bought one yet," I should have written "I haven't bought a Rem 1187 Youth Synthetic in 20 ga yet." I have several SGNs and first trained w/Clint Smith w/SGNs back when he was doing his ITC "road trips" before opening Thunder Ranch (TX), so I know what SGNs can and cannot do. We had several women in that class and a couple of women regularly participate in my club's 3-Gun matches (using 12 ga semis). It takes very little training to learn use a SGN effectively w/in a dwelling.
If home invasions are common where NOPTPARS lives I'd Rx keeping that SGN stashed behind something (like a couch near his favorite chair) where he spends most of the evening and then taking it w/him to his bedroom when retiring. I'd also Rx getting a pistol, something between .38spl/9mm and .45acp, to keep upon his person at least while at home.
NOTPARS, once you have a gun, the main things are knowing when to shoot (law & tactics), knowing how to shoot (training), knowing where to shoot a person (anatomy), and be willing to shoot (moral indignation/outrage).
As far as answering the door, unless you know them or are expecting them (e.g., UPS), why do it? If they say they need help or their car broke down, just tell them through the door you're happy to call help, road service or the police for them -- that's what I've done (at 2 am).
I would much prefer even the 5" dia pattern from a .410 @ 30' (typical "down the hall" distance) than a single 0.35" dia bullet (the true diameter of .380 bullets). A single SGN hit w/20 ga buck will give the BG a LOT more holes to bleed out of faster than a HG, thus preventing BG from doing more bad things. Multiple pellets make hitting a major blood vessel more likely too. Also, as Clint told us, if a BG comes at you w/a knife and you shoot him w/a HG you're hoping he'll drop his knife. If you use a SGN you can blow his knife arm (or head) off. SGNs, w/buck up close, REMOVE flesh. But note well, even if you blow his heart out, if he is determined (e.g., Moros, drugged up, psycho, etc.), he can still fight for 12-15 sec before his brain runs out of oxygenated blood and he MUST go down.
To really give NOTPARS better advice would require knowing more about his situation (e.g., house/apt; rural/suburban/urban; level of criminal activity in the neighborhood/city; is the weapon for him/wife/both; willingness of him/wife to learn/train; need to carry; lay out of home (esp location of family room and bed rooms); etc.).
NOTPARS, about the best and most current info you can find on the web re. the effectiveness of different calibers and shot/gauges is at WarriorTalk's Terminal Ballistics forum (AmmoLab-David DeFabio) and Tactical Forums Terminal Effects forum (DocGKR).
Good background info can be found at:
http://www.firearmstactical.com/tactical.htm
and esp at
http://www.fbi.gov/publications/leb/2004/oct2004/oct04leb.htm#page_15
although it is focused on law enforcement.
WarriorTalk also has a good forum dedicated to SGNs.