According a story published by the Associated Press, Google has lifted the invitation-only restriction on Gmail (not that they were much of an obstacle at this point) and made the service available to anyone who wants in. The beta tag on the popular web mail service remains though. Gmail was first released on April 1, 2004 on a limited, by-invitation-only basis that for a brief period of time created a "black market" microeconomy for the invitations.
More interesting is the announcement that Google will, for the first time, allow heavy users of Gmail to purchase additional storage space above and beyond the 2+GB of storage provided with the free account. According to the AP report:
Now that Google has more computing muscle, (Google co-founder Sergey) Brin said the company will start selling additional storage capacity to e-mail users with extraordinary needs. Google still hasn't figured out the specifics, but Brin indicated the e-mail storage and fees to be introduced later this year would be similar to Google's photo-hosting service that charges $25 annually for 6.25 gigabytes and $500 annually for 250 gigabytes.