When I enter the DC# it says there is no information available and I sent it on 08/07!
If you used the Automated Postal Center, sometimes the DC# doesn't "appear" in the system until the package gets delivered. I think it makes a difference whether or not you fill out the DCN form yourself or have the machine do it (my friendly PO guy told me that when the machine asks if you have a DCN form filled out, say No! That way, the machine generates the # and prints it out on the label).
If you didn't use the APC, I don't know what the deal is- the number should be on your receipt because they scan it in at the PO.