According to Appleinsider, MobileMe push should occur instantly from the cloud down to the desktop even though it only syncs every 15 minutes the other way around. They claim it uses Back To My Mac to do this. I have BTMM turned on and it is functioning, but I don't get updates sent to my desktop unless it syncs.
"However, updates are pushed down to Leopard desktop apps, typically within around ten to fifteen seconds of making changes from the web or on the iPhone. Updates pushed to the mobile are similarly fast.
This unique desktop push feature uses the same Wide-Area Bonjour mechanism used by MobileMe's Back to My Mac for remote file and screen sharing. For this to work, the Mac desktop must first be securely registered into Apple's Dynamic DNS server by simply turning BTMM on (which happens when you install the MobileMe update, if it's not already on). This then allows the MobileMe cloud servers to target updates to the machine as required without the desktop system needing to initiate the transactions. BTMM also automatically configures an encrypted, point to point IPSec connection to secure transactions over the Internet."
Anyone actually see instant pushes from MobileMe down to the desktop? I tried it by updating an event on the me.com calendar.