Did you notice how, in Oblivion, pretty much everyone said 'Hi'? From the Imperial City to Skingrad, almost all non-enemy NPCs, when they walked past you, would stop and say 'Hi' or 'Hello' or something. No matter what look or profession, it was always the same thing.
They'll continue to go about their business, occasionally glancing over to look at you rather than standing in place like a statue as you stare at a close-up of their face, as was the case in Oblivion.
I was reading that in a 1up article, and I thought it'd be a really nice, easy to implement and rather understated feature to have NPCs just having different reactions to you, not based on who you are but who they are. For instance, in a city, some will say hi as you pass them, others won't. But imagine in a very small farming town, with just a few people, or a market town; everyone will have a smile, and greet you in a very friendly manner, because they're a pacific community. However, in other areas; maybe further north, or in smaller communities that are more war-like, obscure, etc, don't. They ignore you, or just grunt something.
I know this is very, very small, and probably used in other games, but it's one of those things that'd really add atmosphere. You'd really feel the change from where you're safe and welcome, or where you should be moving on swiftly. It would even make getting friendly with those more cold communities that much more pronounced, and satisfying.
Just a thought. Hi, I'm new here...