I wear flip flops a lot at home, so I usually wear them on vacation as well and I have no problems.
The place I used to work (abercrombie & fitch) wearing flip flops was part of the dress code so I wore them for about 7 months straight!
I usually get blisters on my heels from sneakers, so flip flops work out great for me. I always bring a pair of sneakers just in case, though.