Okay, I've been looking at code and poking around, looking for bugs and small holes and the like (my apologies to the gods for those who may noticed slightly odd things in the logs.

So here is what I've found... Guest User is not locked out of the following superdocs:
  • Node Heaven. Since it is listed as a level power... right now we have it looking like if level >=1 Can levels ever be zero? We could add a line between 4 and 5 like

    return "Where are you going so fast?  You have not yet begun to live.  Why not take a crack at life?" if getId($USER) == $HTMLVARS{guest_user};
    

  • Node Heaven Visitation. Between 6 and 7 we'd lock out guest user with similar code.
  • Everything Email Options. You get this when you view it as a Guest User:

    Here's where you can configure your Everything Daily Report... but only if you are logged in... ( )full html ( )URLs and Titles ( ) Node titles

    Not good. Lines 38-40 are executing. Maybe toss in:
     return if getID($USER) == $HTMLVARS(guest_user)
    Before hand.
Other than that, Guest User seems pretty much locked down, more or less.

N-Wing says: ok, did all those boring changes :)

Update: In the sense of reusing writeup space, I'll add a couple of more here.
  • Guest User (and other non-edev users) can get to the new scratch pad (you may want to patch that up)
  • In the new /msg me section of a user's homenode, Guest User can see the form, even if it doesn't really do anything.