The hype machine is spinning up quite the storm around this release. That's a great thing IMO, but it's a double-edged sword. If the service is not up to the mark on launch, it will be a huge nail in the Microsoft coffin (no one uses Apple's MobileMe service because it is a dud). People's memories vis-a-vis "Software As A Service" products is very long-lived, and Microsoft would do very well by learning from the mistakes of Apple.
With this being said, this is the first time I am craving to be on the beta list for a Microsoft web service. That has to count for something, right? :)