Be a little suspicious of even emails from people well-known to you if the subject line seems a little out of character for them. Sometimes, they've been infected with a virus or worm program that sends out messages to people in their address book, attempting to spread the virus or worm further. This can be done without them even knowing it's happening, in some cases. The Pretty Park worm does exactly that, using Microsoft Outlook or Outlook Express, every 30 minutes. We are currently evaluating some methods of adding extra layers of security to our systems, including the use of programs called firewalls, which are designed to restrict accesses to only authorized people.
Attachments are still the weapon of choice, but the extensions now include .vbs and .shs.
Be very cautious with opening attachments in general. The advice about checking with the sender before opening an attachment is even more appropriate now. There's something else you can do to help yourself. Change the file view configuration on your system so that you see the entire file name. In some systems, known file extensions are not shown in the folder listings, allowing files with double extensions to go unnoticed.