Despite this New York Times article's (link from the International Herald Tribune; the original Times article was called "Helping People on the Move Keep Addresses Up to Date") claims to the contrary, Plaxo (previously mentioned in this post) is not Google. Google is a search engine. Since most Internet journeys begin at a search engine, Google became a part of everyday life. Updating contact information is not something I do every single day. In fact, if my contact information changes, the only people who do not know are those people who I do not want to have contact with; it's a simple, effort-free way to disappear.
Also, part of Google's success is through the fact that you do not have to join. If I do not use the Outlook family of email clients (which I do not), or am using another computer, it becomes difficult to use Plaxo. In contrast, Google works everywhere (even on the moon).