In one of the best examples of bad launch planning ever, Google Analytics was forced to close its doors to new users shortly after announcing free web stats for everyone last fall. Google will be checking IDs at the door though...only those who receive email invites will be able to register for new accounts.

From the site:

We've added enough capacity that we are re-opening signups on an invitation basis. Many of our users who previously submitted their email address to us will be receiving an invite shortly. As you may know, we experienced extraordinarily strong demand shortly after we launched last November. To ensure a high quality user experience for existing customers, we had to temporarily disable new signups. We have been working diligently to add more capacity that we can both enhance performance for existing users and re-open signups to a limited number of new users.