(1) all ubiquitous systems should default to harmlessness.
(2) ubiquitous systems should be self-disclosing (e.g. be clearly perceptible, “seamlesness” must be an optional mode of operation). proposal of 5 different graphical icons to disclose capabilities of an object (see first image above the post).
(3) be conservative of face, so that ubiquitous systems do not unnecessarily embarrass, humiliate or shame their users.
(4) ubiquitous systems should be conservative of time, not introduce undue complications into ordinary operations.
(5) ubiquitous systems should be deniable, offer users the ability to opt out, always & at any point
(via the rather excellent Information Aesthetics)