We don't have any plans to add support for a commercial/residential address selection. We should always obtain the Residential rate for any live rate-lookup method, as most retail buyers would want their order delivered to their home.
I haven't heard word back from Development about the apparent Commercial rates that damndirtyape was reporting, so I'm not sure how to account for that, unless maybe there was a temporary glitch at UPS's end that had their site's rate API always returning Commercial rates for some brief period? Or maybe they always treat certain zipcodes as Commercial? All I know is, we pass the order's origin and destination zipcodes and total weight data to UPS as a Residential shipment, and their site returns a rate that we add to the cart -- pretty simple process, really.
Make sure you configure each product with an accurate Weight that includes any packing materials required for each unit of that product, and configure your packaging types with an accurate empty weight, so the combined weight of products and packaging will add up adequately close to the actual weight of the shipment.