Be unique or be a "very quick" follower.

Email from addressbook management websites is a proven tactic in successfully building up a content base.

When Plaxo began, anyone joining the plaxo network would automatically send invites (or Plaxo would send the invites on his/her behalf to all the friends and contacts in their address book - the moment the address book was uploaded to their site.

Other sites simply take notice and copy..

The upside for these companies
1) This giant directory of interlinked people can then be serviced with social networking tools supported by Google Ads
2) more money from the Ads means the side could get acquired

The downside
1) People just ignore the emails
2) The sites are seen as spammers
3) More people leave the site, or turn into non-active members.

You can only try a marketing tactic so many times - and if people have seen it before, they stop responding to it.. Too many marketeers think of marketing tactics in the same way as they see ads - "Use an ad often enough and people will take notice".

This has been proven wrong time and again. Be unique or be a "very quick" follower.