I do a LOT of shipping for my company. Fedex, USPS, UPS, DHL...those are the guys I've dealt with in the past 4 years. I ship about on average 160 packages a day but also send upwards of 2000 packages a day for about a week a month. (no, I don't work for qvc)
I have found Fedex and UPS to be just about right on with their delivery schedules...and both companies 3day, 2day and Next Day services to be right on the money. The fallout is usually on the vendors side.
Common problems I have down here in the shipping hole: Salesperson tells you at 2pm on a Friday that they'll ship your package out and it'll be delivered the next day. (UPS and Fedex do not do Saturday delivery you specifically pay for that service. Costs upwards of twice the cost of regulard next day).
Salesperson makes a sale at 3pm and tells the client it will go out today. I ship the package the next day instead. Why? Because my UPS pickup is at 4pm and I've got better things to do than sit here and click the refresh button on my sales software every 15 minutes.
So, my bet is it's the vendor. Weborders are a real pain in the butt too because there is no feedback from Customer Service. I think I have two outstanding orders that were place on my companies website for out of stock items. I have no idea if my CS dept has contacted them. The orders are in limbo and there's not much I can do about it till it gets in. (CS dept does recieve notification from the system when out of stock items are webordered)