I took a look at the common off flavors page of How to Brew. Astringent seems to fit better than anything else, but only because it lists dry. There's no pucker. I'd say it tastes like beer that's been left out and gone flat if not for the obvious carbonation (and dryness). It's like the flavor has just faded. It's still there and would be not good, but drinkable if not for the dryness.
Happened with 2 bottles the other day and I'm hesitant to open (and dump) more since I'm down to 4 22 oz'ers and a growler. Brought the growler up to sit in room temp for a couple of days and am planning on cracking that open with some friends tomorrow. My dad has a six pack that I gave him for xmas he'll be trying this weekend too. I'll report back with both of our findings.
Thanks again for the assistance. The wealth of knowledge here really helps give us new brewers some additional confidence. I'm also taking comfort in the fact that my second batch was easier, faster, and while young, already tastes great.