It changes my account language to German and causes Amazon to send me a "your account language was changed" email, so it kind of makes me avoid your direct links...
A lot of people, including me, are using amazon.de in English, as they have free shipping to quite a few European countries (and e.g. http://www.amazon.fi/ redirects there).
Thanks for the feedback.
For small purchases I don't care that much (and .de has cheaper shipping to me), but for larger purchases I usually price-compare between .de, .co.uk, .fr, .it, .es, .com as the price difference may be significant (i.e. save me hundreds of euros), and all of those sites have had the cheapest price on occasion.
Amazon.lu (luxemberg) but no amazon.be (Belgium). Amazon.at (austria) but no amazon.ch (Switzerland). No Romania, Bulgaria, Greece, but they do have Lichtenstein, Poland, Denmark. No Slovakia (sk) but they do have Czech (cz).
Not having local amazon blows. You can buy prime but shipping isn't free or next day (best case 3 days usual around 5), a lot of the shows wont show etc. Also random thing will decide that they wont ship from one amazon, but will ships from some other. Also returns are expensive.