I try to get takers on eBay or Craigslist first, but I do use Gamestop as a third measure, or if I'm really itching for a game immediately and need to unload some games quickly for cash. I had to do that for Bleach: The Blades of Fate last year.

I very rarely do.

i do periodically

Rarely... I only sell games I know I'll never touch again. Otherwise I keep them.

I never sold or ever will sell my games.

I used to but not anymore. I sell them at ebay now.

I've never sold a game.  The closest I came was trading an extra copy of Half Life for Red Alert 2 with a friend.

Not worth it....

I keep my favorites and sell the rest to buy new games.

Didn't used to sell games but now I do because they become almost worthless after a year or so and can always be bought back for a couple of pounds if I want them again.

I usually used CEX in the UK, they give a much better trade in price.

For example I took my friends daughter to trade some DS games in Yesterday and was offered:

GAME: £46 cash £62 trade in
Gamestation: ££58 cash £70 trade in
CEX: £78 cash £118 trade in