That's an interesting question. Ford say they designed the ecoboost to last for 150,000 miles, but personally I can't see many 1.0 turbo's lasting anywhere near that long. They have also had it running at 180 bhp.
I guess that the higher the bhp pushed through the turbo the less long they will last.
Might find some answers on the focus and fiesta forums, where they have been running the engine a little longer.
What's also interesting is what the difference is between the 100ps, 125ps and 140ps engines. I managed to find out that the 125 uses a stronger metal part in the turbo but other than that, is it just a question of mapping?