That's very, very unlikely! Of all the new modern diesels I've had, intakes have done nothing more than give a little better sound in most cases.
I don't have one, but if they can say I'll get even 2 MPG better I'd buy one in a heartbeat.
The only problem is, most only come to forums to report issues. The ones that drive and enjoy their EcoDiesel's daily usually don't signup and/or post to report the good things.
Really, we have no way of knowing how many "fail".