We went to Subway in Greece...after a day of walking around for hours and hours, and a breakfast and lunch of some VERY amazing greek food we just wanted to eat dinner in our room so we grabbed subway...I didn't seek it out though.
We did go to McDonalds on our last night, well, I didn't...I had souvlaki in a pita from a little corner shop, my mom and brother tried things in mcdonalds we don't have here. Sometimes it's fun to explore the differences between here and there, even in crappy fast food places. That said, if I was only in a place for a day or a couple meals I wouldn't choose fast food.