I am college student and live in a college neighborhood. Of course there are always lots of parties and drunkards wandering around the neighborhood at the wee hours of the morning and the chances of a drunk, belligerent person wandering into the wrong house is a very real possibility.
Fireman, I feel for your position, having lived in student sections of college towns myself. However, if anyone can wander into your house accidentally then your first, second, (and so on) lines of defense are sorely lacking.
How in the world can a drunk "wander" into your house? I understand how a drunk can stumble up the wrong walk, can pound on the wrong door, can even throw up on the wrong doormat and pee in the wrong flowers. But "wander" into your house? What happened to all the other lines of defense that we're supposed to maintain? Where's the deadbolt lock on the solid entry door? Where are the well-lit approach ways? Where are the strategic rose bushes that make approaching ground floor windows difficult? Security system? Dog? Etc., etc.
I know you're not saying, "Well, the door's off it's hinges and the windows are all missing, and I don't have a security system or lights or even a dog. All I can do is sit here in the dark with my shotgun. Sure hope nobody wanders in 'cause all I can do is shoot him!"
But it kind of sounds a little bit like that.
A drunk college kid is not going to employ the pre-meditated and aggressive techniques needed to invade your secured home. He might bang on the door and yell a lot -- until you explain (from the other side of that door) that he's at the wrong house and both you and Mr. 12 ga. would like him to leave. He might even try to climb up to a window -- until he's a bloody mess tangled in the roses he doesn't remember planting under "his" window...or until Mr. German Shepard tries to bite his nose off through the glass. ("Woah, dude...When did I get a dog?... Belch...Hic!") But he isn't going to breech your door, jimmy your windows, and/or wage a purposeful assault on you in your home. Generally speaking, of course.
Having your home be reasonably secured should give you the time to figure out which thing is happening. Is a drunk jacka$$ stumbling around in my yard breaking my flower pots and knocking over the garbage? Maybe I should call the cops and keep an eye on him from an upstairs window until they get here. Is it a crew of alert and purposeful uglies carrying crowbars and ball bats who just popped my door off the hinges? Maybe I need to respond with force right now -- sooner if possible! A reasonable security "perimeter" should protect the drunk idiots from getting far enough in to risk their lives -- and give you a bit of warning and time to assess the situation.
All that to say, if you need to shoot, you need that first shot to be the most effective thing you've got because you might not get a second one. And if you really didn't need to shoot, it won't matter if you were loaded with marshmallows and candy kisses, you just committed assault, aggravated assault, or manslaughter.
There's no such thing as, "Oh thank goodness I'd only loaded rubber buck -- that was just party boy Jimmy from next door!" Party boy Jimmy would be dead with a load of rubber buckshot in his head and you'll be facing a very different life ahead.
Keep your buckshot, buy some locks and lights, get a dog, develop a "hardened" (or at least better congealed!) perimeter. That will save a lot more frat boys' lives than your rubber buckshot.
Just my humble opinion, of course.
-Sam
EDIT: Just read your response to RP88. If you've got the door unlocked and folks coming and going frequently, please just forget home defense with the shotgun. You have no safe zone. If folks don't need to break in order to gain entry then your legal justification for shooting at them at all is a LOT harder to prove. What if the rubber buck does the trick? What if you made a mistake but they're out of the hospital in a few days with some bruises? You just discharged a firearm at them, UNJUSTIFIED. You'll be in jail for a lot longer than they'll be healing up.
EDIT2: The door is always locked when no-one's home? Well, if you keep it locked, at least you won't mistakenly shoot any frat boys who try to get in your house ... when you're not there...;-)