I believe the reasoning for the snippets not working in the comment block is that the parser ignores everything between the comments.
In regards to the list of additional snippets, here are some more:
code = code.Replace("$DATE$", DateTime.Now.ToShortDateString());
code = code.Replace("$TIME$", DateTime.Now.ToShortTimeString());
code = code.Replace("$USER$", Environment.UserName);
code = code.Replace("$MACHINE$", Environment.MachineName);
Red Gate Software Ltd.