I just wanted to second this -- getting a UPS Store mailbox is much better than a PO Box, if for no other reason than the fact that you can receive UPS/FedEx/DHL/etc. packages there. The post office won't sign for packages from 3rd-party carriers, so you're out of luck if you want to have anything shipped to your business address of record.

That being said, neither a UPS Store box or a residential address is exactly going to impress folks if they bother to check out your business address before decided to ink a deal with you.