Well, you get 1GB of storage, to begin with. That's 10x what most free services give you.
It's "special" right now because it's invite-only; it's still in beta. I don't believe there is a date for the gold version yet.
The reason the invites have been so popular (like on eBay, etc.) is because many people want to reserve their name as soon as possible, to avoid addresses like thiswastheonlyoneleft909822004@yahoo.com .