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

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.

I use a subsonic filter, -3dB at 8 Hz., 24dB/octave. I use it when I listen at loud volumes. It can be switched in or out through a tape monitor type circuit.

I do not use one or needed one. Haven't had that problem in about 40 years. As the quality of my turntable went up. Typically it is a resonance problem with your turntable or compliance mismatch between tone arm and cartridge. Perhaps there are some other possibilities. But look at your turntable and setup to find the problem. 

@dwette 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

@ghdprentice But look at your turntable and setup to find the problem. 

+1 best to chase down to eliminate the feedback than to try to filter it out