I actually won the March CAG giveaway, but I wanted to wait till I had more than two weeks experience with Goozex before weighing in with my opinions.
The Goozex community has been great, I've had a couple dozen trades total (sent and received) without a hitch so far. The system to talk to people you are matched with works well (i.e. ask if they have received the game yet, or explain you are shipping later than anticipated). The people that run the site are very responsive to any questions you may have.
I'm glad I gave the site a try, investing a few old games risk-free (they will reimburse you points if the game arrives broken or missing, I think) and getting new games to play in return. My friends I have invited have also had positive experiences.