Is it ok to wire light switches and lights with 12/2 cable?
As long as you have a 15A circuit breaker on that circuit, it's OK to use 12/2 NM cable for your lights.  Since the maximum current on the circuit will be 15A, you won't need special switches.  You should label the wire that it is 15A, not 20A, so that someone else doesn't come along and treat it as a 20A circuit.


Pro: 12/2 cable is a slightly better conductor of electricity, so you'll have slightly less loss between the service panel and your fixtures.  
Cons: it's more expensive, harder to work with than 14/2 cable, and you may need to use larger junction boxes because the NEC allows fewer 12 gauge conductors than 14 gauge in a given volume box.  


You'll probably also find that you won't be able to use the insertion fittings on the back of the switches (but that's OK, IMO, because I always use the screws), and you definitely won't be able to use the electrical nuts that come with your lights, so you'll have to get your own (and making a secure connection might be trickier with 12 gauge).