Q: will it damage your computer if you leave it on over night
A: No, there will be no damage to your hardware. In fact, it is BEST to leave the computer on 24/7 if you can afford the cost of power. However, some will disagree with me (servers run 24/7) As for software, depending on what you are running, RAM might get depleted over time (as you open and close programs and not all RAM is returned and made available) and cause a crash (blue screen sort). XP is decent about this. Vista...still deciding if it is good - just went to SP1. I do not have any experience with Macs. I leave my HTPC (XP PRO) on 24/7 for the past 10 months. This does not mean it has not been turned off - I schedule maintenance to defrag and scan disk once a month at 3AM. Once a year I tear it apart and clean it because of dust build up.