Excellent and intriguing answers thus far, thank you all!
I am personally of the "i'd rather it be cheaper" mindset with my own purchases.
There are factors that concern me like weather, as Hector mentions. I am in South Carolina where it's 900 degrees, 11 months a year. The heat is always a consideration.
Sticker shock is my biggest concern. I currently divide the US in half by the Mississippi river. East is a flat rate of $6.25, west is $6.75 (Free shipping once you pass the $45 mark). This covers the postage and my service and label fees. I have tried my best to keep priority mail as low as it can be (I often lose a few cents, depending on where the customer is). However, if you are ordering one soap only, your bottom line price jumps by 50%. This bugs the crap out of me.
When I finalize orders and i'm at the screen where I can choose which shipping option, a lot of the time, as Steeleshaves mentions, First Class has the same delivery time estimate as Priority. Since I've been really paying attention to this, it's never been more than two additional days.
Lots to ponder. I'd love to hear more of your thoughts.