Does OS X Notification Center receive messages from APNS, LAN or just locally? I'm looking for technical details on how the Notification Center is architected on Mountain Lion so I can make the most use of it as a user of OS X. Specifically, does it receive messages directly from Apple's push notification service? The high level overview documentation on Apple's developer site for Notification Center mentions UDP delivery of a notification so it seems a network trigger is provided but I can't find a reference to or example of this being implemented on Mountain Lion.

If not, can it receive messages from the local network or just from other programs that run locally on OS X?
It can work in a couple of ways. One, as you say, is through APNS. 

Apps can also use the local notification centre to trigger a notification (you can see this in XCode when a build completes for example). 

What are you trying to do? Maybe I can point you at the right document.