You guys are talented coders but I don't think you've ever actually SOLD and SHIPPED anything using your own store's USPS Calculated shipping.
Choosing which box size to use according to weight is quite possibly the WORST way of calculating shipping costs. You just made your USPS shipping module useless.
This one feature is basically holding me back and keeping me with eBay (who does calculated shipping and rules VERY well).
Let Me Explain:
There are a lot of products that are large but light weight (like the giant calendars that I'm selling and need to be shipped flat) and lots of products that are small but heavy (my other productsl). Your USPS module doesn't make any sense by associating box size with weight. It doesn't work like that.
I should be able to specify a box size for EACH product.