I also travel quite a bit overseas and within the U.S. Just as the others before me, I have never been asked for any Medical I.D. or doctor's note. However, I do carry a doctor's note with me at all times. I also have a cardboard fold-up wallet insert that came with my glucometer in which I can list my meds, dosage, doctor's info, & emergency contact info. I just carry this with me at all times because you never know who will be knowledgeable in case something should happen when you are not around people familiar to you. But, I have never had to pull this out, unless I have to update the info on it. :oD
The only problem I've ever encountered with traveling and diabetes was with my fashion Medical ID bracelet. (see my post under the group Traveling With Diabetes: http://juvenation.org/groups/traveling_with_diabetes1/forum/t/6388.aspx)
Best of luck and have fun!