I was there today, and the deal was going still going on. I asked the clerk when it would end and she said on April 14th, though with this actually only being an extension of the one that was suppose to end around Easter, it could actually end at any time.
So, now's your chance it seems. I've traded in about 12 games so far for a little less than $100 in credit. Not sure what I'm gonna use it one (Jade Empire maybe?), but it's good to have.