BTW Skeet, I'm a liddle anal so on two of the benches I've poured I've isolated the legs from the slab (you'll see it referenced in the gallery if you look closely) but on the others I've just poured everything touching or even monolithically. The monolithic pours were for freestanding units.
So far, of 6 tables, the smallest of which is 25,000lb, none of them wiggle under foot traffic.
My main shooting bench, right outside my gunroom, is framed of wood setting on the slab floor. It's plenty solid but a big guy standing directly behind the shooter and stamping his feet hard can make the crosshairs wiggle. This is on a good base, the slab was poured over a subgrade that had been rolled in with a 100" vibratory highway roller.
al