Non-US Vendors and Customs Duties?

[Kevin24]

I've been seriously considering buying some things from Non-U.S. based sellers like Kamakura Shirts and Herring for while. However, I've read of people who have bought from these websites being hit with pricey customs duties and fee's once their goods arrive.

For example I've read i about Canadian's who order stuff online from overseas getting hit particularity hard

However, since I'm in the US I was wondering if it's common to for one to be hit by customs duties when ordering from overseas? As I couldn't get a clear cut answer from the Customs and Border Protection website about this.