I really wish that option would be off by default.
That crap doesn't help stop viruses from spreading. My folks run an online business. As a result, my dad emails thousands of people. For the first few years, he had NO idea that every single person he emailed was being added to his contacts(this was also a setting in Outlook Express, not sure if it still is). Then they got hit with a nasty worm and it sent itself to their entire contact list.
Remember, use adequate protection and practice safe e-mailing.