Is this wrong?
When someone leaves something at your house, and you keep forgetting to give it back every time you have an opportunity, and at last you just keep it (without using it, would that be wrong?) because it would be awkward to give it back, and well, he probably forgot about it and doesn't really need it anymore.. :-)
well... consider another situation where they had forgot it but... they need it very badly and they are searching it for that everywhere.. So in this situation its necessary to get the thing back... I do remember a quote "Better late than never."
So.. it totally depends on teh situation the person who left it in your house be.
I don't consider this as wrong:)