Just a heads-up: If you subscribe to MSDN or TechNet, you can now grab the slipstreamed ISO for Service Pack 1 + Windows Server 2008 R2 or Service Pack 1 + Windows 7.  There is a standalone Service Pack installer there as well (It's only listed under Windows 7 for some reason, at least on MSDN.)

The public release is next week, on February 22.