I've travelled with my 1ds3. It's no fun when you have a big white lens on it. Big and heavy!!! However, I've learned that coupling my 1ds3 with a lighter lens like a 16-35, 50 1.4, 24-70, or 24-105 makes it tolerable for travelling. I wouldn't say enjoyable, but I would say tolerable. I guess it depends on what type of traveller you are too. I walk a lot when on vacation, whether it be adventure treks or urban walks, and I definitely like a smaller, lighter setup. If you include a car on your vacations, then a 1d body setup is less bothersome. If you're a backpacker or like to travel light, you won't appreciate travelling with a 1d body. I whole heartedly recommend travelling with a 5d or a Rebel body instead. My last trip through SE Asia (adventure/backpacking), all i brought was an Olympus e-p3 and simply loved life. My current travel setup is a Rebel t3i, 15-85, and an S100 (for restaurants and going out at night). Sometimes I replace my s100 with an x100. To summarize, for me, it's about light weight and mobility... so I leave my 1ds3 at home when I'm visiting the rest of the world.
One last note... in one incident while shooting with my 1ds3, I've been asked to stop taking pictures while people around me were allowed to continue takings pics with their p/s.