Priority Mail is the biggest joke of a scam every launched upon the citizens of the United States. I mailed two packages priority mail to two different locations on 12/12/08 and they didn't not arrive until 12/24/08. Yeah, 2 to 3 days....NOT! It costs about 50% more but what are you actually paying for? They don't guarantee it so I guess you paying for them to try to get it there on time but they don't do a very good job of it. And, they can't track it unless you purchased the tracking feature which is extra.
Go Fed Ex or UPS. The tracking number is included with anything you send, even ground. And if it doesn't get there in the time paid for they refund your charges (they have for me).