No matter if you're exclusively a Windows shop, every good IT technician needs Linux in their toolkit. A bootable Linux CD has saved my bacon more than once.
I'll start with something simple, but yet undoubtedly an issue that is faced by somebody, somewhere every day.
It's the problem of the forgotten administrator password. You have a Windows box but can't log in. Nobody remembers the password. Or, you can log in as a regular user but can't make changes - because nobody remembers the administrator password.
http://www.linuxlinks.com/portal/news/article.php?story=20090309134524317