I think M$ is doing something with smoke and mirrors in Netlogon to make it possible. Howard has confirmed that in AD, a startup script can in fact write to Netlogon. Now I wasn't sure, and never tested, if it holds true for any other share but this thread seems to bear out that Netlogon is "special".
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Give a man a fish and he will be back for more. Slap him with a fish and he will go away forever.