I like your idea of using block helpers to limit access to certain parts of a view.

I describe an alternative approach to checking permissions at the ActiveRecord level in my post RestFul permissions in Rails

def admin?
current_user and current_user.admin?
end

if admin?
xxx
end

Thing.create_from_params_if_user_can(current_user, params[:thing])

why should all things know about the user, let the user know what he can or cannot, so the knowledge is at one place(and mostly the logic is the same, so everything can be handled in an case statement)

Thing.create(params[:thing]) if current_user.can_create?(Thing)

and in the views, the new link is only shown if the user can create this thing

The idea is outlined here: http://pragmatig.wordpress.com/2008/06/29/separate-rights-management-from-controllers/
and some helpers that are based on this concept here: http://pragmatig.wordpress.com/2008/07/09/generic-smart-link_to_s-link_to_edit-link_to_destroy/