A new white paper has been published on how Microsoft IT has used Virtualization (naturally Hyper-V) and consolidation to reduce cost, server sprawl and at the same time improve scalability, standardization and uptime in the SQL Server environments.
It is an interesting read, with some really detailed designs and metrics, that you can base your designs on.
You can find the white paper here: http://technet.microsoft.com/en-us/library/dd557540.aspx
One key take-away is that the underlying storage really must perform well. Storage performance is one of those topics that has been highlighted many times in the past, but never receives the attention it deserves. No matter how good your design, unless the storage performs optimally, you will never good SQL Server performance.