Do you leave your computer on??

Why do we always leave our computers on?

This is a very pertinent question, especially now in this era of 'going green'...so why in the IT industry as well as in some non-IT industries, why do IT departments in general encourage leaving PCs on all the time?
As the article says, take some time to read ALL the pros and cons. Also note that the articles about 'Green Computing' have not generated much interest: 8 comments maximum between them all?? Most of the articles on TechRepublic pull in 20+ comments on average.

Soooo, what's your take on it?