If you use Plaxo you should have received an email from them stating they have changed their privacy policy and terms of service, the biggest of which is their decision to share information with their "partners".
As it is outlined in the email:
1. Demographic portions of your data (such as zip code, gender, or industry) and usage patterns may be shared with our trusted partners who deliver advertising to you on our behalf. Consistent with our current policy, personally identifiable information (e.g. your name, address, phone number, email) will not be shared with third parties for advertising purposes without your consent; and
2. The advertising networks who deliver ads on Plaxo may use their own cookies to collect information about a user's activities across their entire network of Websites.
It is a slippery slope when companies start "sharing users information".
