A number of people have asked:

Is there a way to customize the existing code metrics or add additional ones?

The simple answer at this time is No.  There are no extension points or customizations available at this time for code metrics.  This feature was added late in the cycle for VS 2008 and we were out of time to design and add the required hooks. We will use this release to gather feedback about the sorts of extensions you want. 

To that end please feel free to respond to this post with information about any customizations or additional metrics that would be of interest to you. This will help us a lot in our future planning.