I've always run gentoo system with -O2 because I always thought a few packages might fail on -O3. however today for no apparent reason I decided to switch to -O3. I cannot believe it! It actually made a very noticable speed increase on apps as small as rox, urxvt, coreutils. So I'm currently re-compiling all my favourite apps -O3. I'll post again when I get round to OOo and X and see if they fail.