I've rooted cuttings anywhere from 1" to 3'. Development seems to have more to do with the vigor of the variety than the size of the cutting.

cuttings root at each leaf node, so a longer cutting has more places it can root, and more roots make a stronger plant. i use cuttings of different sizes, but try to sink most of what i start with in the pot. i root cuttings in sand in the biggest plastic pots i can afford. i cover them at first with clear plastic coke bottles, with the bottoms cut off. because of the large pot size, i can leave them as long as i need without hurting them.

I root 6 inch cuttings in a clear jar of water on my patio.

Do you guys scrape off the stem underneath the node around the whole stem? SOmetimes I notice is right there where it begins to turn briwn and roots never occur once it turns brown.

I use six inch pots or so and the cuttings are about 6-8 inches long. I try to have at least two nodes below the soil, and one or two above it.