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

Most "audiophile" phono pres don’t make this a switchable option, or really even make clear what they’re doing. The original RIAA spec is flat to 0Hz. Some stages probably use this. RIAA IEC modified this to add a high pass at 20Hz. Other stages probably use this. The IEC spec is not a very steep filter - definitely helps a bit, but it’s not going to save a bad configurations on its own (bouncy floors, crappy racks, subwoofers nearby etc).

The KAB Rumble filter is a different beast and much much steeper than IEC or anything I’ve had built-in to a phono stage - it can in fact save bad configurations. The question is whether you find it sonically transparent or not for audible frequencies. That said if your woofers are flapping wildly, no question it’s better to use a KAB until you get the mechanical issues under control - which ideally you would do anyways. Electronic fixes are more of a band-aid. 

@mulveling 

My Boulder 1108 does have a button. It's described as a 3-pole (18db/octave) low cut filter, with response of -3db at 10 Hz. When I asked a former Boulder tech person about it at my dealer they told me I shouldn't need it under normal listening circumstances. I have yet to find a use case where I feel I even need it. Record warps are inconsequential to me since I use a 750 gr record weight and 1500 gr peripheral ring. That's enough weight to make Dolly Parton flat.

For owners of sealed box speakers it is less an issue, but since the advent of vented speakers it can be a big help in controlling woofer overexcursion. 

Even though I have a vacuum-hold down turntable, there are some records that will cause subsonic rumble. I do use the filter under those conditions and thus will always buy a phono stage that has a filter.

@dman777 

First, if you carefully match your cartridge's mass and compliance to that of your tonearm you should be able to achieve an optimum vertical and horizontal resonance of between 8 and 12Hz. This is precisely what you do to ameliorate the effects of record warp information being amplified and sent to your speakers.

Rumble is a characteristic of a poorly designed main baring or one that has been "modified" and contaminated with foreign matter as opposed to just leaving the original permanently lubricated one alone.

Many phono preamps are designed with a gradual and progressive roll off below 100Hz which leaves the response down by 5 - 10 dB at 10Hz or so and forego an adjustable subsonic filter. Probably most of them.