The motor that was in the car when i bought it had done 3000kms on it and failed within a month doing no hard driving at all.
My current motor has done 20000km's, ~15 track days, 2 drag days and over 100 dyno pulls (Built by Dan @ ERD in July of '08). Running on BP Ultimate / Shell Vpower all its life. No fancy fuels here.
Shit happens thats out of anybody's control (faulty parts), but in the end if your builder/mechanic knows there stuff, and you don't cut corners, you can get a lot of life out of them.