I've had a Mac Pro for 2.5 years. I've never run diagnostics or de-fragged the HD like I did with my old G4. I called AppleCare to ask if I should do this periodically (I have the Tech Tool "light" disk that came w/Apple Care, and I often hear ads for $99 Tech Tool Pro). He asked if my drive was slow or having issues. I said no. While there apparently is no Apple party line on this, he said he never uses Tech Tool. He showed me how to empty the caches (also never done, 9,000 files deleted) and sent me on my way. Just wondering what others think about running diagnostic/de-frag software. Thanks.