Out of curiosity what filesystem are you using on your servers? I assume many of you are using whatever your VPS provider is using by default, but for those of you with full control over your installations, do you have a preferred file system, and if so why?
Personally I've been using Reiser4 on my installs. The default ReiserFS support in the Linux kernel is sort of slow and broken, but with the unofficial patches I find I have much better overall IO performance with Reiser than with EXT4 or JFS. My only concern with Reiser4 is that Hans Reiser was jailed for murdering his wife and his company Namesys is now defunct, so there really isn't much in the way of support anymore. Real shame.