We know that product activation can be a very complicated thing to figure out for developers, where environements are constantly torn down and rebuilt, and activations are not unlimited.
I was just alerted of a few more resources that you may find useful:Product Activation in Development Environments for Windows 7 and Windows Server 2008 R2
Converting KMS Clients to MAK - required since Windows 7 and Windows Server 2008 R2 install automatically as KMS clients. A MAK can be installed during or any time after operating system installation.
And as always, if you are wiping and rebuilding more often than 30 days, you may want to consider not activating at all since many products allow usage for 30 days prior to activating.