Coninental out of Newark is so tight you can rarely book a seat last minute let alone change flights -- which inplicitly ruins a key benefit of premium fares -- flexibility.
CO is very tough to get premium availability inside of 2 weeks on EWR-SFO/LAX, which is part of why I think that PS needs to be expanded to EWR as well. (But CO also charges <half of what UA does for PS..)