I just ran across what I think is a newly published white paper on parallel processing in SQL Server 2008 R2. The date is October 2010 but this is the first time I have seen it so I am not 100% sure how new it really is. Maybe you have seen it already but if not I recommend taking a look. So far I haven’t had time to read it extensively but from a cursory look it appears to be quite informative and this is one of the areas least understood by a lot of dba’s. It was authored by Don Pinto and Eric Hanson with a supreme case of technical reviewers as well. So here’s more bedtime reading 
http://msdn.microsoft.com/en-us/library/gg415714.aspx
Andrew J. Kelly