From Major Nelson on the forums:
As you all know from the previous announcement (view post 7032451) Today (4/21) we are upgrading Xbox Live to lay the foundation for new features. While you won’t see many of these new features until games support them, I wanted to tell you about a new feature that you’ll be able to experience immediately when the service is back online later today. The first thing to I need to tell you is there is NOT a major dashboard upgrade, but there is one feature that you’ll see that I have not announced until today: Voice Messaging! After today’s upgrade Xbox Live members will be able to send and receive friend requests and invites from the dashboard with a short voice message attachments. As games begin to adopt voice messaging, you’ll be able to send/receive voice messages in game, but for now the only way to use voice messaging is in the dashboard. After the upgrade, give it a try!
Sounds pretty neat. I have to admit I forgot about the downtime briefly today but then figured it was a great opportunity to play some single player Pandora Tomorrow. Great great game!! The player movements and transitions are superb! It really builds on the experience. I think its my new favorite (For this month anyhow).