Thanks for all of the fun advice, friends.
It's comforting to know that I'm not the only guilt-ridden Baptist/Protestant out there :-)
Chad called Publix this evening while I was watching Cady. They said they'd take the yogurt back or something to that effect. So, before we went to see Michael Moore's documentary on Capitalism (a blog for another day), we headed to Publix to return the yogurt. Of course, Chad thought I was ridiculous. He took the yogurt in and deposited it on the customer service counter, informing the nice person working there that his wife's conscience wouldn't allow her to keep the free yogurt. I think they both got a laugh out of it.
Still, I don't think that Publix really cared (I mean why should they care about $6-ish worth of yogurt?). The sense Chad got from talking on the phone with the folks and taking the yogurt into the store is that it wouldn't have really mattered if we'd kept it. BUT, if it wouldn't have mattered, why didn't they just tell us to keep the yogurt? I would have kept it gladly. My kid can eat her weight in yogurt. And, I mean, we did have to drive all the way back to the store because of their mistake. I had to remind myself that I would have driven back if they'd overcharged me (and I have) so I should be willing to do the same when it works out in their favor.
Anyway, it's over now. I'm ridiculous. I know.