Seriously though -- my memory of people is kind of average. And by "average", I mean that I can easily remember people I've had brief conversations with, even if those conversations were a year or more ago -- but I won't remember what those conversations were, or who the person is. I'll just know that I must have seen them or talked to them once!
Regarding conversations more recently than a year ago -- say, a few months ago -- I can remember some little random details about them, I can remember what the person look like, but like other people on this thread have said, context can be an issue, and remembering people's names is always a struggle.
My theory about the problem in the OP is that a lot of people (myself included) really hate forced conversation, and all conversation with someone you either know nothing about or have nothing in common with is forced conversation -- so if you pass by someone you vaguely remember from somewhere, you might rather pretend like you don't see them, than see them and say hi really awkwardly. So it might not even be that they don't remember you.
Re: Si and this sort of thing... Based on my Si experience and observing the Si of others, I think my Si picks and chooses what it remembers freakishly well. Conversations are not included in this group, but music and popular/artistic culture is. If I play a video game start to finish, I will remember almost everything about it -- I will be able to sing to you start to finish most of the game soundtrack, I will be able to quote it obscurely, and I will be able to continue to do this for years and years of my life without playing the game again.
... and yet despite this I still suck at remembering people's names.
I'm excellent with names and faces, (and some other memory stuff-but particularly this-) to the point where it creeps others out. I often remember people on one quick transaction. Then they see me in the grocery store like, "HI JOHN!" And they are like
06/13 10:51:03 five sounds: you!!!
06/13 10:51:08 shortnsweet: no you!!
06/13 10:51:12 shortnsweet: go do your things and my things too!
06/13 10:51:23 five sounds: oh hell naw
06/13 10:51:55 shortnsweet: !!!!
06/13 10:51:57 shortnsweet: (cries)
06/13 10:52:19 RiftsWRX: You two are like furbies stuck in a shoe box
I'm not good with faces and this can be embarrassing. In the workplace, I'll be assisting a customer and then the customer comes back several minutes later, and I won't always remember my interaction with that person. I guess most peoples faces just don't stand out that much to me. I do better when there's some distinctive feature about their face to latch on to. I rely alot on visual cues other than the face such as hairstyle, glasses, or body shape to aid in my identification of someone.
5w6 or 9w1 sp/so/sx, I think