A new whitepaper has been published that comprehensively covers the Resource Governor feature of SQL Server 2008, written by fellow MVP Aaron Bertrand and SQL PM Boris Baryshnikov. I read through this a while back (but didn't have the bandwidth to do a full technical review) and it's an excellent whitepaper with lots of code examples and in-depth explanations.

Check it out at http://download.microsoft.com/download/D/B/D/DBDE7972-1EB9-470A-BA18-58849DB3EB3B/ResourceGov.docx.