I prefer UK to US even if it's a little more expensive because their service has always been so good. That's not to say I don't buy stuff from US.

I don't buy books from Amazon though. I like to request them from my Planet Books and pay that little extra more because they provide me good service and I enjoy spending a lot of time there. I don't ever want to see it out of business. And at the end of the day, when I do a price comparison with other bookstores (even Borders), it's still cheaper. That's not to say I don't buy from other bookstores, I just prefer PB. I like to inject a little business there.