My personal take is that they just wanted to make sure that
 *everybody* is keen on getting an account. Make it exclusive,
 by invitation only. Seeding it amongst the geekest of geeks,
 first generation invites went quickly. But seemingly invited
 users got their own share of invites.

 Now it has become a practical test for the claim that every two people
 in the U.S. can build a chain of mutually known persons of maximum
 length 6. If that is true, how many invites per person would you need to
 reach saturation?

 Make people sign up and store their information on your company disks?
 Easy. Instead of crawling and begging them for their data, be a snob
 and make it a challenge for them. They will fall for it.

 On my box I have gobs of gigabytes for email storage, no ads
 and a very fast interface via procmail, formail, mutt and grep.
 I will not entrust a company with a service I can provide just
 as good.  I will be the last one without a Google email address.