I have several pads for several purposes now.
2 of the white foam pads (one came with the PC, one extra ordered) are used (and labeled, each in their own respective baggy, with some breather holes poked in them) for Machine polish #2 and Machine polish #3. I bought a Griots orange foam pad that I use for Paint cleaning stage. The Griots red foam pad I use for final waxing stage.
Cleaning the polish out of the foam pads is quite easy, but cleaning wax is another story. I found out that using alittle Dawn will strip out all the wax in a pad. Make sure you completely rinse it out and press it dry when your finished.
A set of pads will last you a very long time if you just take the time to care for them. Do not let any product dry out on your pads. Clean them immediately after using them, if your finished with that particular pad for whatever phase of your detailing you are in. Then "bag" them. this prevents dust or dirt imbedding in the foam pad, thus creating a nightmare on your finish later on. Be sure to aerate the bag so mildew or mold doesn't build up (or dry them completely, then bag them until the next use)
I highly suggest the little 3" foam pads (to be used by "fingers") that Griots sells. These are a must for getting into tight spots like the bumper areas. I bought two of them, one for Fine Hand polish and one for wax.