IIRC the "named user" license is mesured at (what Oracle calls) the multiplexor, so in the case your database is powering a website, each named user would be each user at the webserver (I don't remember reading a distinction of anonymous -i.e. not authenticated- vs authenticated requests.
So for the web I would recommend that you go with the processor unit.
The "power unit" (i.e. per MHz) type of licensing stoped when Oracle introduced 9i IIRC.
So now you pay according to how many processors the machine that runs Oracle has or the "named user" type of license.
Just in case, the licensing tips from the Oracle store might help clarify things.
