Nope. When I did my extended business trip to Texas (late 2007/early 2008) I was able to order stuff from Amazon.com using my UK credentials and have the items shipped to office I was in at the time. It was lovely buying new cameras and lenses at not much more than half their UK retail prices. Also, if you travel through a state with no sales tax, any Apple store will be glad to help.

Do make sure the guarantee or the Apple Care agreement covers you internationally though.