This Technical White Paper was published by Microsoft March 2009:
SQL Server Consolidation at Microsoft
The document is rather interesting as it in a structured way describes what we as concerned and dedicated DBAs thinkabout when we have a spare moment...
I like the Servers Ratings based on CPU usage (p 7), as it is a simple and yet effective way of rating the existing SQL Server installations. The existing monitoring tools in the infrastructure such as Microsoft System Center Operations Manager (SCOM) or Idera SQL Diagnostics Manager (SQLdm) will have the historic data needed to rate the existing SQL Server installations.
The three consolidation approaches (p 7) are also usefull. I only miss an approach like "Network Consolidation", to handle a needed segregation of duties and environments and still manage the entire enterprise SQL Server platform.
In general the half hour spend reading the paper was worth it.