Public role permissions

Hi,

As public role being mandatory role to all users, I wonder
is it wise to deny some permissions from it. For some reason,
public role seems to have select-permission to system tables
(to sysobjects for example). I don't want users to have
access to our metadata.

And very weird was, that it had execute permissions to some
user-built stored procedures, though I haven't surely granted them.
(Unless they have been granted by system while transferring objects
from 6.5, I don't know.)

I'm using 7.0 and Books Online said almost nothing after
searching 'Public, role'