When playing an unaligned character consider this quote from the phb1 page 20: “If you’re unaligned you don’t actively seek to hurt others or wish them ill, you also don’t go out of your way to put yourself at risk without some hope for reward. You support law and order when doing so benefits you. You value your own freedom without worrying too much about protecting the freedom of others.” I interpret this as an unaligned character is not likely to preform acts of outright evil such as killing a PC (A friend of theirs who has fought with them in many battles). I see an unaligned character as being a typical everyday human, somewhat selfish but not selfish to the point of evil!
If a unaligned character does preform an act of evil (small or large) and is spotted by a fellow good PC I do not believe a truly good PC would immediately turn and attack his friend and ally (not without repeated offences). I believe before it escalated that far the Good PC would be shocked and would attempt to question the unaligned’s motives, judgement and possibly request he repent or make amends. I do not believe allies who regularly watch each others backs would come to blows other a stolen trinket or an insulted lord.
The above writing is available in the help section along with a link to a discussion on unaligned. After I wrote this message I thought it important enough that I decided to make a log post of it. It is likely I will also post links to other articles in the help section regarding this subject.