Former Apple product guru Jean-Louis Gasseé pins the responsibility tail on the MobileMe donkey in a long blog post [1] in which he describes the machismo that leads to playing chicken with launches. Gasseé writes, "No one had enough brains and guts to risk humiliation, to raise a hand and say: Chief, we're not ready here, let's stop everything. As a result, MobileMe badly crashed on launch."
He goes on to explain why sync is hard, and why it's easy - despite Apple's many years in providing a kind of semi-working sync that I had many problems with - to underestimate the complexities of live reconciliation and coordination. Gasseé believes that Apple didn't eat other people's dog food: they didn't learn why BlackBerry is called Crackberry, and how Research in Motion (RIM) developed a reliable system that's used so broadly. RIM spent a decade tuning the system to where it's at today.
Gasseé was a critical figure at Apple in the late 1980s, and he had a heavy influence on the firm's product development. Through the 1990s, he ran Be, which developed an operating system that had many admirers (although few users) and some influence on Apple.
[1]: http://www.mondaynote.com/?p=783