My Dad recently got the following email (excerpt only).

You should be alert during the next days: Do not open any message with an attached filed called "Invitation" regardless of who sent it. It is a virus that opens an Olympic Torch which "burns" the whole hard disc C of your computer. ...

While the Invitation virus is a hoax, the message is likely a good one. If you don't know an attachment isn't a virus, then it's better to be safe than sorry.

• Don't send images as attachments, get a Flickr account and send them with Flickr.
• Don't send videos as attachments, get a YouTube account and send them with YouTube.
• If someone sends you images as attachments, then tell them about Flickr.
• If someone send you videos as attachments, then tell them about YouTube.

You are either overly cautious or prone to get viruses.