I was eavesdropping on a conversation between a couple of the smartest SQL Server MVPs around - Adam Machanic and Kent Tengels.
Kent pointed out the new query processing team blog at http://blogs.msdn.com/sqlqueryprocessing/archive/2006/09.aspx. You definitely want to check this out.
In addition, Adam mentioned another blog done by an anonymous team member at http://blogs.msdn.com/craigfr/Default.aspx. This is a well-written and in-depth blog with lots of great informations.
I encourage you to subscribe to both.