That's a misleading headline; there's no indication that the "sync" feature will be any more Dropbox-like than any of Microsoft's previous attempts at sync (like Groove, or Windows Live Sync, etc.)

Sync is so-well-known a problem at Microsoft that Joel devoted an article to the "architecture astronauts" wrapped up in it back in 2001. In fact, we're two weeks from the 10th anniversary of that retrospective. http://www.joelonsoftware.com/articles/fog0000000018.html

EDIT: Actually, this 2008 article by Joel adds more to the story: http://www.joelonsoftware.com/items/2008/05/01.html