I estimated that I had used my mac for approximately 10 hours a day, 5 days a week, 48 weeks a year, for 7 years straight, for a total for whopping 16800 hours. I have written the first versions of most of the software components of my startup using this computer. And all this time, this machine worked without a hiccup. It was never repaired, and I never opened the back cover. — Cleaning My MacBook After 16800 Hours of Use!