The announcement mentions that those already connected to PlayOnline will stay connected, but once you disconnect you won't be able to access PlayOnine until the maintenance is finished. So, 360 Final Fantasy XI fans (both of you) better connect now before it's too late.
Update: Reader bigC24 let us know that the Live outage is official. Check out Major Nelson for details.
At the following time Microsoft will be performing maintenance on the Xbox Live service.
For more information please see the Xbox Live official homepage (http://www.xbox.com/live).
The PlayOnline Viewer will be unavailable to Xbox 360 users during this time. Players already logged into Playonline will be able to continue to use PlayOnline services. However once logged out, PlayOnline will not be accessible until the maintenance period is over.
We apologize for the inconvenience.
Jun. 27, 2:00 to 6:00 (PDT)
Users of the Xbox 360 edition of the PlayOnline Viewer