None of the panniers I have used have been waterproof, although all were (somewhat) water resistant. My tendency is to seek shelter when the rain starts, and wait for the storm clouds to pass. Nevertheless, I have been caught in heavy rainstorms and been forced to press on.

I have no complaints about water-resistant panniers. I keep items that must stay dry in plastic bags, anyways. Other items near the walls of the panniers get a little damp, but they also dry out.

The panniers I bought last year at Mountain Equipment Co-op include waterproof covers that fold up and slip into an inside pocket. Not a bad compromise.

Circa 1989, I bought a set of Cannondale panniers, made of tough Cordura nylon. They were beautifully designed and built, and lasted about 15 years. The waterproof coating on the inside began to de-laminate after eight or ten years. I compensated by spraying the exteriors of the panniers with an aerosol water ******ant, which extended the life of the panniers a few extra seasons.