I may be mistaken, but I believe lots of normal people just make do with the stock rubber feet components come fitted with ;-). It has been argued that a component "voiced" with it's stock rubber feet won't sound as it's designer intended with other feet, if in fact those after-market feet change the sound.
The thing about rubber feet is their ability to isolate is not linear, but rather frequency-related. Garden-variety rubber is pretty effective down to maybe 10Hz, the frequency at which it's isolation-capabilities are in sharp decline. That is why rubber (including Sorbothane, though it is available in a range of durometers) is known to cause soft-sounding, smeared bass.