What is the norm? How many of you use the subsonic filter with your turntable?

My phono preamp doesn't have one. I guess I've been lucky as I never have significant woofer excursion on my 10" sub or the 6.5" mid-bass drivers. I am even using a DD table in fairly close proximity to my speakers. Maybe it's the concrete floor that helps. Perhaps you're experiencing some tonearm/cartridge compliance issues. 

I have a full-range speaker system (IRS Beta) and no rumble filter. VPI TNT III sits on a VPI stand. No rumble, no feedback.

I agree with others about using rumble filters. If there isn’t a problem with warps or bad mastering, woofer pumping is a sign of setup issues. In that case a rumble filter is a band-aide that does nothing but – maybe – mask the problem.

In many cases using effective isolation for the turntable can resolve issues.

Years ago I had a tonearm with magnetic bearings that caused woofer pumping. It was the wrong arm to use in my environment. Once I changed it to a gimbal tonearm with mechanical bearings the issue with woofer pumping disappeared instantly and completely.

I now use a HRS rack and isolation base for my turntable. Nothing upsets the table now.

sometimes. 

I also have a Hegel V10 phono preamp and don't use the subsonic filter.  My SOTA turntable (with vacuum holddown platter) sits on a special heavy shelf in my Target stand, so there's no need for a subsonic filter.