I guess the basic concept would be like this:
Good:- People trust you more easily, opening 'good' quest lines and giving bonus on persuasion in some case I guess.
- Good and neutral vendors will offer better prices, at least if you helped someone they know perhaps.
- Everyone evil will be hostile on sight, some evil will have enforced their groups or locked away their treasures.
Slightly good aka Neutral aka Slightly evil:- You always get the option to demand rewards.
- Neither side will be automatically hostile just because of your 'fame'. There still can be other reasons like 'Magisters'.
- You have access to all vendors. Being 'slightly' might have positive or negative effect on the prices tough.
Evil:Same as good, just the other way around. Gives of course other persuasion effects because you are more intimidating and less trust worthy.
Pure evil:- You are so infamous, even the evils are afraid of you. Both good and evil forces will enforce themselves against you and be hostile on sight.
- Only few vendors will still be available for trade, because they don't bother being undead, demonic or whatever.
- Normal NPCs will flee your presence.
- Perhaps pure evil questline from the chaos god or so?
=> Evil deeds are always of bigger impact, than good ones. Fullfilling a good quest line but later killing the quest giver will mostlikely give you more evil than the quests gave you good for example.
The alignment does not depend on reaching a specific number of good or evil, but on the comparison between 'good' & 'neutral' & 'evil' deeds you did.
But I guess, it will be hardly implementable in the actual game without heavy overhaul.
