I didn’t know there was an old one, but Major Nelson just posted there is now a fancy new Xbox Engineering Blog:
Welcome to the new home for the Xbox Engineering Blog. This is a place where the Xbox development team will communicate directly with you. We’ll share information straight from the people that develop, test, manage, release, and maintain the Xbox 360 and its services. I am a part of this team as a software development engineer in test, working on community features such as friends and parties, and I am happy to introduce you to this new space. As with the previous blog, my co-workers and I will continue to share tips and tricks about the Xbox, and give you a closer look at the people and science behind Xbox 360. We’ll start off by giving you a behind the scenes look at some of the technology that went into recent releases of the Xbox 360 system software. You can expect to hear from us about a couple times a month.
http://www.xbox.com/en-US/live/engineeringblog/default.htm
Worth keeping an eye on.