I received a software update from Apple last night for MobileMe.
MobileMe is synchronized computing in the “Cloud”, where you can keep all your mail, calendar, contacts, documents, etc. in your MobileMe Account and all your devices stay synchronized from that central global location, whether it be your Mac, PC, iPhone, or iPod Touch.
MobileMe pushes updated information to your other devices so you don't have to manually sync the information ( unless you prefer that method which is optional ). Per the Apple Website:
“MobileMe stores all your email, contacts, and calendars in the cloud and keeps them in sync across your iPhone, iPod touch, Mac, and PC. When you make a change in one place, MobileMe pushes the new information up to the cloud, then pushes the change down to your other devices. Choose a sync interval for your Mac or PC. On your iPhone and the web, sync happens continuously.”
Being that MobileMe is from Apple, you know it will support all the Mac products, like iCal, Mail, and Address Book, but it also has support for your Windows PC applications like Microsoft Outlook, Outlook Express, Windows Mail, etc. And, of course, it works with your iPhone and iPod Touch versions of these applications as well. You now have synchronization for all your desktop applications and mobile devices.

Even cooler, however, is that there is a website version of your favorite applications at Me.com, so you can access all the information as well as send mail, update your calendar, manage your contacts ( Address Book ), manage your online file storage, etc. via a web browser. I haven't played with the applications extensively, but they look just like the slick UI on the Mac and have that Web 2.0 flare to them.
Apple has some videos and other information about MobileMe on its website here.
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