Sub users...

Depends on the crossover point. If you are using the sub to just augment the lowest notes (30 hz and below), then one sub in mono can sound very natural. However, if you are crossing over substantially higher--say 60 Hz or above, then 2 subs in stereo will sound more natural.

For 2 channel music I personally use 2 subs, but they are in mono and rolled in at 30 hz. The 2 subs are used to flatten out the room modes.

Rives summed it up well...I also use 2 subs to even out the modes and to enhance low end weight and impact below 30hz which is where my Sophias begin to roll off:O)

Bass frequencies are sent to both channels in 99.9% of mixes. Below around 100 Hz you cannot tell where a sub is anyway (if you can it is because leakage of higher frequencies - you can use a steeper filter in the case of a poor quality distorting sub). Your fear is really unwarrented if you intend to get a high quality subwoofer and correctly match it with your mains.

If you buy a ported boom box of a subwoofer then it will indeed ruin Dave Brubeck but not because drums will jump around but mainly because of masking from all the bass resonance and poor transient response from a cheap sub. The most expensive driver on large mains is usually the big woofer. The hardest and most energy demanding driver on any speaker is the woofer and the LF. Logically you might expect to pay as much (or more) for a subwoofer as your mains in order to maintain a similar level of quality.

Thank you all for the great replies. While I have not researched subs, the JL Audio F113 is the one that has my attention. I would be using it to augment the lowest notes as you hint Rives, 30hz'ish and below.