I have never been declined using CapOne cards abroad, from charging expensive hotels to gas station to metro tix. Of course, I always call ahead of time with a list of countries I am visiting and the trip dates (though I hear this doesn't work for everyone).

Now I did get 2 calls from the fraud dept. after charging $3k worth of tix from Orbitz, but that's another matter and they didn't decline the charges, just verified.