What obligation do we have regarding post dated checks?

This may be addressed in UCC. I remember something about the customer having to give the bank advance notice about the post-dated check and the customer not wanting it honored until that date.

As a payor:
You are not liable for paying a post-dated check as long as you pay the item in good faith. (UCC 4-404) Given the automation of the payment process, the maker would be hard pressed to shwo that you did not use good faith, unless they have notified you of the fact and have asked you not to pay the check before XYZ date. If the maker makes such a request, make sure you charge the appropriate stop payment fee.