I recently had to replace my HD on my three-year-old iBook G4. The Apple Store employee said that using one's computer "day and night" definitely causes wear and tear on the HD. Guiltily I thought about my habit of falling asleep while playing movies on my laptop--sometimes very long DVDs, like complete seasons of shows, so the DVD is playing for several hours (after a day of regular laptop use, e.g., e-mail, creating docs., etc.) Do I have to forego the DVD habit or risk ruining my new HD? If DVD-playing does wear out the hard drive, er...how fast...?