Well, I was interested. I thought it'd be nice to see how it fares while playing Dota 2. Then I read this on the FAQ page:
Free to play games drop game cards based on your in-game purchasing. For every $9 USD spent (approximate) since the start of the Steam Trading Card Beta, you will earn one card drop.
I'm notably less interested for the time being in light of this. I still need to play Portal 2, though, and I do enjoy some CS:GO from time to time. If nobody is in a hurry to take you up on your offer, I'd appreciate a beta invite. I'm just not dying to get in on it with particular haste.