Infrequent thankfully.Of all the nightmare scenarios,this one takes the biscuit and requires immediate landing(if possible).As 411a rightly says,it helps if you have a a good F/E.
Indepth response to smoke whilst airborne should only be attempted if you have no way of getting down asap.Primarily,it consists of donning O2 masks/goggles,establishing communications,and setting up for an approach and landing at the nearest suitable airport.This is esp true for a 2 man flightdeck.On a 3 man flightdeck,the checklists are more in-depth and allow for more detailed trouble-shooting.If you dont have the Immediate land option on a 2 man flightdeck,then its down to improvisation based on airmanship and systems knowledge.This would include depowering and/or isolation of busses or electrical items that are classed as usual suspects,eg,recirculation fans,equip cooling fans,galley power(first to go).Pilots should know ALL items in the electrical smoke&fire and smoke removal checklist and how to isolate certain electrical busses.From memory.Cb's can be reset after 2 min cooling period,but some would wisely ignore this option.
Delays due to fuel-dumping or establishing radio contact with company should be avoided at all cost.Land overweight and call company on your mobile after landing.