PA Castle Doctrine
I am not a lawyer, but the PA Castle Doctrine gets a lot of discussion in the PA Firearms Owners Association discussion boards. The presence of an intruder does not, as far as I know, give the homeowner the right to just blindly blaze away; but forcible entry of an occupied dwelling, with the emphasis on forcible, gives rise to the assumption that the person who has entered is a threat. Leaving your front door unlocked and having somebody enter is not necessarily assumed to be a threat unless that person is confronted and refuses to leave. At that point, if I remember correctly (and I am NOT a lawyer so I may be wrong), the person who is trespassing and refuses to leave becomes a hostile intruder. The discussions on PFOA generally revolve around there being no need to retreat, unlike SS215's statement. In Philadelphia proper, the DA may decide to prosecute anyway, but if there is enough press generally has not done so in cases where a homeowner is confronted by an intruder.
I did live in MA during the era of "you must retreat if possible." The DA in the Boston area at the time was Newman Flanagan. One of his successful prosecutions of a person who shot an intruder even though there was a possible retreat was overturned by the appeals court. It seemed that the appeals court believed that even though the man could have retreated, he was not obligated to leave his 14 YO daughter upstairs and undefended under the law.
Moron Lave (send a Congressman through the car wash)