Of course, I don't think the author's intention was to claim that Context_Info was the solution to all of our security concerns. I think he merely chose that as an example of how to use it.
I wonder if you can change Context_Info repeatedly within a stored. Perhaps you could use it to output debugging info or something like that. Don't you hate when you have debugging statements in a procedure, but they don't get output until the procedure completes or fails? Maybe this can be used to output some debugging info as it runs. I don't know, just a thought.