+1 for this. I was just bitten by this last week, when I switched from using a custom container where size() was an int to a std::vector where size() is size_t.

The code was check-all-pairs, e.g.

  for (int i = 0; i < container.size() - 1; ++i) {
    for (int j = i + 1; j < container.size(); ++j) {
      stuff(container[i], container[j]);
    }
  }

Which worked just fine for int size, but failed spectacularly for size_t size when size==0.

I totally should have caught that one, but I just couldn't see it until someone else pointed it out. And then it was obvious, like many bugs.