> Integer overflows are so rare that I can't even remember one happening with 64-bit values. Underflow on the other hand... I've encountered that plenty.

I totally agree!

After some horrible bugs caused by unsigned integers in innocent looking C/C++ code, I'm 100% in the signed camp. The only time I use unsigned is when I need well-defined overflow behavior (which is rare).

As a bonus, using signed loop counters in C/C++ code enables certain kinds of compiler optimizations (based on the fact that signed integer overflow is undefined behavior): http://blog.llvm.org/2011/05/what-every-c-programmer-should-...