There is often one for each side (the boom and the pedal). Same for the snare (top thump and bottom metal spring thing)
I didn't know that. You learn something every day. I'd still say that, for the novice home recordist, you wait for a while before you try this kind of thing. Plenty of home guys get great kick sounds with one mic. They don't use anything fancy beyond getting a good source sound and putting one mic in the right spot.
Any time you use two mics on a source, you create the *potential* for phase problems.