Because I ride ten or twelve different bikes during the course of a year, tracking mileage is impossible. I use a Park chain checker. Not surprisingly, my chains almost never wear out. I just don't put enough miles on any single bike.

I've read reports that some of the new ten speed chains wear out very rapidly. I wouldn't know. Four of my chains are the wide one speed/three speed type. The rest are mostly the six speed/seven speed type. Keep up reasonably clean and lubed...they last a long time.

Just one more reason I don't think I will ever buy a ten cog bike.