lukslo: Sorry if it didn't come across, that was meant as a sarcasm.
In my opinion is just another excuse to make more money (market) and let's be honest, probably people will buy certain games only because of the trading cards.
edit:
Exactly as Pheace said, some will value collecting the cards others just won't try to bother and sell them for some steam wallet credit.
In the end it's up to the user to decide what to do.
And yes, you can sell cards in the market.
I'm glad there are some more people thinking like this. I just read some stuff about trading cards and thought to myself "what a load of crap"... But then again, they won't do any harm, except for possibly being addictive. And I remember being somewhat more interested in "achievement stuff" in the past, although this still seems a bit overdone to me.