I've done 3 full trackdays and a ring trip on the current set (not driven to/from). They still have tons of tread left. It really does depend hugely on driving style though.
Make sure you keep hot pressures 30psi or less (cold - very low 20s front, mid 20s rear). I personally run them at about 28-29 hot. If you run them higher than that you'll wear the centres down in a day.