15 amp sockets and code?

Yesterday I got a call from someone asking about how to 
wire up some sockets and lights in a basment remodel.
The specific question was about the breaker size since
the box the outlet came in specified a 15A breaker.
I asked what guage wire he was running and since it was
14ga told him to use 15A breakers.  

Now the question.  Has the code changed in recent years
to disallow 15A (NEMA 5-15) outlets on 20A circuits, assuming
of course the circuit uses 12ga wire?  I know there used
to be specific exemption for 15A rated outlets on 20A wiring.
Have they taken that away, or was warning on the box some
legal CYA?  Just curious.

Bill Ranck
Blacksburg, Va.