This is quite possibly a fake, although none of the features are specifically ground breaking so there is no reason why it couldn't be legit.

The information from Engadget is as such:

• The update hits May 7th
• Your contact list will now integrate Windows Live Messenger, and show joinable session status
• Messenger contacts can see what game you're playing, and your gamertag
• Marketplace will now have its own blade, which will be skinned independent of your theme
• Users will now get inline achievement updates
• Low-power download mode and auto-shutdown
• You can watch partially downloaded movies
• You can text chat messenger six friends playing games watching movies
• Multiple tweaks on the user interface

The only thing there that really effects me is the inline achievement updates as I do find myself hitting the guide button every time I get an achievement to see what it was and how much I got for it.

Anyway as this is just a rumour we will just have to wait and see. The only thing I would really like to see come to the 360 is the movie service coming to Australia, but I can just keep dreaming.