Last week I presented three different sessions at TechEd and used my laptop to run at five different Virtual Machines at once in order to demonstrate various Windows Server 2008 technologies.  The performance of Hyper-V was amazing, but I tell you I wish I knew of the Performance Tuning Guidelines for Windows Server 2008 document before I presented.  I just took the last ten minutes reviewing the guidelines for Hyper-V and have already jotted down a few things that would have helped my VM's performance.  The guide is not exclusive to Hyper-V though.  In fact it's got all sorts of goodness in terms of tuning up your Windows Server 2008 boxes for optimal performance.  I highly recommend downloading and reviewing this guide if you are deploying and using Windows Server 2008.