Actually I use Plaxo...then everyone has to only keep themselves updated
I joined because my boss asked me to so she could link to my contact information. I like that you can set it different for business/family contacts ie home email/address/phone vs. business, etc. Plus, if my contact info changes I just update it and everyone else who I'm connected to will automatically update when they access me in their addressbook. So I only have to keep track of updating myself.