[Hays]

Most of these, more people should be aware of them :

http://support.microsoft.com/kb/126449

Very helpful, bookmarked that page.

[windir]

Most of these, more people should be aware of them :

http://support.microsoft.com/kb/126449

I was forced to learn a lot of these keys when my mouse broke and had no money to buy one xD It is extreamly helpful to navigate through your desktop with just the keyboard. Quicker too on a laptop!

[barcode119]

If you have a mechanical keyboard and your esc key is a lot closer to ~ than usual, hitting ctl alt esc is a fast way of bringing up task manager.

[edwardj7337]

Very nice thread.
#3 on the OP's list should be mentioned to all novice computer users.

[Choddie]

Why never to open spam mail?

• When you open spam mail this sends a signal back to the sender alerting them that your account is active. This is good news for the malicious hacker or marketeer. So it's best to delete without even opening.

How can you tell when somebody has opened an email?

//edit
html email communicating with their server? :S

[Choddie]

It's a feature called "tracking", most POP3 email clients have it, and so does web-based mail client.
Here's an example for Gmail :

Cool, interesting stuff. Thanks for the source.