Overall I'd say it's fairly rare. There are several reasons for this.
First, foam is expensive. A five gallon drum is about $100 to $200 depending on the concentration (either 3% or 6%, 1% is not allowed for ARFF purposes). Note that that's the pure foam, which will yield much more than 5 gallons when mixed in with water. If I remember correctly, the Striker 1500 fire truck holds about 200 gallons of pure foam, so you're talking between about $4,000 and $8,000.
Also, it takes a long time to refill. So say that you foam one portion of the runway, but the plane doesn't land exactly there, or it skids off onto another unfoamed section. If you spent all your foam already, well now you don't have any left over for the actual crash.
This is an interesting quick read on the subject here
. The FAA specifically warns against attempting to foam a runway with Aqueous Film Forming Foam (AFFF), which is the style of foam most widely used (by a very large margin, I would imagine), in ARFF trucks.