I haven't used any, but have thought about it. The one that I did look into was too much.
I have found that if you shop around to a few different places you can usually find one that has a decent shipping amount, and still save $.
I have just rcvd some work boots, and have in shipping some other clothes and some rotors and pads for the truck.
The worst thing about it is the little bit of extra wait, but if you can order in advance of needing anything you still come out on top.