Steve Rachui just posted some great information about R2's unknown computer support on his blog: http://blogs.msdn.com/steverac/default.aspx
My favorite quote, that I think bears repeating, is:
"Before using this feature stop to consider that this can introduce unwanted image deployments to the environment"
If you're interested in learning more about R2's unknown computer support, check out these posts:
Unknown Computers in SCCM 2007 R2 – overview
http://blogs.msdn.com/steverac/archive/2008/09/21/unknown-computers-in-sccm-2007-r2-overview.aspx
Unknown Computers in SCCM 2007 R2- how it works
http://blogs.msdn.com/steverac/archive/2008/09/21/unknown-computers-in-sccm-2007-r2-how-it-works.aspx
Happy unknown computing…
~Jeff