I have taken the steps necessary to absolve shippers of any responsibility for leaving things at my door. UPS, FedEx, Airborne, and DHL all have the paperwork from me that says it is OK to leave things at my house. I live pretty far away from anyone else so it's really unlikely that something would get stolen off my porch, though of course it is possible.
For UPS not to just leave a package there have to be explicit instructions from the shipper not to accept the on file paperwork that allows packages to be left at your door. If a vendor is going to require that you sign for their packagaes, regardless of how innoucuous they are, they should tell you that up front so you can take your business elsewhere. If UPS won't leave the package, then its unlikely to get delivered, and I'll stop payment on the credit card and re-order from someone else. The vendor won't get any more business from me.