Moral Dilemma

Since cjk stole my thunder on the post he just made, I'll have to settle on something else equally interesting. And this situation is ultimately all about me, which is a good thing.

I recently bought a new laptop from Lenovo which I'm expecting to arrive by X-mas. After I bought it, the pending charge showed up on my bank account letting me know that while there was $X dollars there, about $600 of it was supposed to go away very soon. I checked the account this morning, and the $600 had magically reappeared in my "available balance."

So...what is the moral action in this case? Do I contact both Lenovo and my credit union to let them know something's up? Or do I just say, "Hey. They screwed up. And I get a free laptop out of it"? And if the first choice is the moral one, does that make the second choice immoral?

I have an idea of what I'm going to to, but I'm going to wait a week to see if the situation resolves itself. And I'll obviously pretend the money isn't there. But...what would you do?