Interesting article up on Code Project:

"The principal advantage is that, the user can still register and use the COM server even if he is not an administrator of the machine or does not have write access to HKEY_LOCAL_MACHINE. "

http://www.codeproject.com/w2k/regsvrex.asp

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... and another technique that someone clued me in to: http://www.red-gate.com/other/com_without_registration.htm