Michael (another PM on the XNA team) has followed Mitch's lead and bypassed his blog to add a ginormous post directly to the XNA team's blog.

His post:

The XNA Framework Content Pipeline

provides the best overview of the Content Pipeline made available so far.  He also added links to a demo of the pipeline that he gave at Gamefest. Thanks Michael!

Shawn Hargreaves also put out a collection of more informal musings on the Content Pipeline. If the density of Michael's post gives you the shivers, walk through Shawn's posts and then give it another go.

A dribble of background assumptions
Splashing around on the surface
Diving deeper
The way is shut

However, as Shawn notes, the Content Pipeline won't be released as part of the initial beta. This information is being made available to give us all a better feeling for the motivations of the XNA team and to get a sense of where they're going.