MacRumors has discovered that though you receive your MobileMe email very quickly, the "pushing" of other MobileMe services is not as fast when coming from your Mac. Apple's knowledgebase article states:
Selecting Automatic in Mac OS X allows your computer to immediately sync and update when there are any changes on the MobileMe servers. Those changes can come from your iPhone, iPod touch, the MobileMe website, or another computer. Changes made on your computer will be synced to the MobileMe "cloud" once every 15 minutes (or every hour in Mac OS X 10.4.11).
Automatic is not so automatic anymore. You can always manually sync your calendar, contacts and bookmarks, but if you leave it alone, it could take as long as 15 minutes to receive your updates on your device.
I have personally not experienced this. Even when I change information on my Mac (specifically iCal), I received the updates in a matter of minutes. I suppose this could have been because my scheduled 15 minute sync was about to happen, but I really have not noticed that much of a delay over all.
What do you think? Is this really that big of a deal? Should Apple's push services be realtime from your Mac?