- last post: 01.01.0001 12:00 AM PDT
There's no direct harm in not signing out; the only effect is that it leaves a cookie on your machine so your login information is retrievable automatically when you revisit the site. As such, it's possible to read it in if you knew what to look for, therefore your login info (username and password) are not as secure. Whether you're comfortable with that is a decision all your own.
As for not turning the computer off, it's an extra chunk of money to the electric bill, but not bad for the machine so long as your fans are clear and the machine can stay relatively cool overall. My last 3 computers ran night and day and I've never had one fail in any way; they've only been replaced with newer models when I felt it necessary. Likewise, the machine in my office has been turned off (excluding immediate resets and power-ons for updates) no more than four times in the past year and a half with no issues whatsoever.
[Edited on 9/23/2006]