I have replaced it twice (have it on one bank only), both times it lasted probably a couple thousand miles.
I noticed this when i had the car dynoed, the dyno shop lambda showed a different A/F than my UEGO unit, about 3 points richer. So the sensor was still working but showed it was running LEAN, while the dyno lambda showed it was OK.
There are many causes to premature sensor failure, high exhaust temps, leaded gas, rich mixture, thermal shock (like tons of water coming into contact with the exhaust).
In theory they can last as much as 80k miles, but in my case i have probably fouled them because one of the above reasons, most probably running rich (first sensor), thermal shock or high exhaust temperatures (625 RWHP).
I have seen this happen to others, so i only extern that it is better to only have them in place for tuning or maybe while racing to extend their life.
Rob Hernandez, AFM co-Founder.