Yup, i've done both and then some.

my car is a daily, and a good stereo is a must have in my life. I'm not a basshead, i just like good quality sound. So it may seem that i went all out on this system, but actually i held myself back quite a bit. After all the s2k is a sportscar first, and a convertable, so it doesn't make a heck of alotta sense to pour thousands of dollars into a system that is consistantly battling road and car noise. My minivan is another case, however.

Here's my system today:
Alpine 9833 headunit
Alpine KCA420i ipod controller
Focal KP2 compnent fronts
Phoenix Gold 600Ti powering the fronts
Diamond Audio D6 10" subwoofer in a sealed enclosure in the trunk
Another Phoenix Gold 600Ti powering the sub.
Infinity reference speakers in S-pods powered by the headunit.

The S-pods are great, if it's the only thing you do it enables you to hear the music with the top down at speed.

If your goal is better sound: over power your fronts to create a great front sound stage, and use the rears for fill. This way, the spods to create a "fuller" sound for your stereo.

all in all, the spods are great mod.