Actually, if you install the iCloud package on Lion, one of the things it installs is push notification services.
If you use Find My Mac, you can force a push notification to be sent to you Mac. It looks like a normal UI window with the close, minimize, and resize buttons missing and two selections - “Ok” or “Cancel.”
EDIT: I looked up the actual process I had seen installed. It’s called “aosnotifyd” and has been around for a while - primarily used to push MobileMe info about mail, calendars, etc. to the Mac. This might mean I’m totally wrong, unless Apple is going to build push notifications ontop of this delivery service?