I just recently traveled in Europe and got (my U.S. passport) stamped in every country, even when leaving for London from the Munich airport at the end of my trip. Didn't have to ask once, though I probably would have.

I think the reason for that, though, is because I was crossing into and out of the area covered by the Schengen treaty. I was stamped at the Prague airport (after arriving from London), at the Austrian border (on the train from Prague), and at the Hungarian border coming from Vienna. I also got re-stamped coming back through Austria to Germany, but not at the Austria-Germany border, which is pretty much what I expected.

Now, to steer this thread in a slightly different direction: Does anyone know why the immigration officer at Heathrow the other night wrote what appears to be a "72" in pen on top of her stamp? I explained to her that I had a flight scheduled to JFK the next morning. I also had a previous LHR stamp from seven weeks prior. I have a theory, but I don't want to prejudice any possible answers.

Back on topic, I'd like to add that I was too cool for school to ask for a stamp once at CDG, and regretted it (hence my later request). Also, I have a Canadian stamp in my passport, which makes a friend of mine actually jealous. But he's a massive Canadophile.