I traded my Gamecube in when the DS lite was released. I traded it in with ten games, my old DS, a Gameboy SP, and five GB games. I got the new DS Lite, two DS games, and about $120 leftover credit.
I haven't played a single GC game on my Wii (unless you count Zelda: TP and Super Paper Mario...zing!).
My End of 2008 Hardware Predictions (console only):
Wii : 50 million
360: 28 million
PS3: 24 million
These predictions were made on January 3rd and won't be revised