I was under impression that, at least on gcc, everybody uses -O2 and -O3 is reserved for those who have the patience to verify that their software not only still works correctly, but even actually becomes faster.<p>FWIW, I once tried -O3 on some number crunching code few years ago and results were mixed. Improvements, if any, came from only one or few of the many -f flags enabled by -O3.<p>Oh, and I also tried -O3 on Gentoo. Some weird gtk crashes, had to rebuild back with -O2.