I've offered races outside the core rules/PHB (for C&C and D&D, specifically) for almost as long as I've been running games. But I can probably count on one hand how may times a player has chosen a "non-standard" (meaning not in the core rulebook) race for his character. Likewise, I can't remember the last time I played a non-standard or non-PHB/core book race.
What's your experience. Have you offered races outside the core book? Have they been chosen by the players? Why, or why not? As a player, have you been offered additional races? Have you played them? Why or why not?
For me as a player, I think for me it's concept. When I know I'm going to be a player in a game, I immediately start thinking character concept. And my brain usually gravitates towards a PHB race for some reason. Probably habit. This has often happened because I'm informed of my position as a player before all options are given, so I have a standard race in mind before optional rules are known. That's my theory, anyway.
I tried to make this question appeal to players and GMs, so I could get opinions from both sides of the screen.