I have about 20 copic sketch markers that I have been buying individually at a local art store. I am not particularly talented in the "coloring" area, so like any other medium, these require practice, experimentation, and it helps to have some talent too! I don't go out of my way to get them (but the store is next to my grocery store!!), so I happen to drop by once in a while and get a few ...
I am using my prismacolor pencils a lot (mainly without the gamsol) and want to really get better using those and also watercolors before I try my hand at coloring in images with the copics. These are pretty expensive and there isn't anything magical about them -- I don't find them easier to master than anything else, but I know that I've seen some amazingly beautiful things done with them, and I speak only for my result! I think if I could go to a class to teach me how to use these it would really help a lot.
That said, the copics have a couple of features that I think put them in another class and make buying at least a few of them worth the $$$ --
1. you can use them to very easily color brads, embellishments, etc. including ribbon! I also used them just to change the color of the background of some printed paper from white to cream. Got to love that and this is why I think it is worth investing in some of these.
2. the copic air brush system looks so cool. I don't have it, but I want it. The sketch markers are the only copics that will fit into the copic airbrush system. I think that makes the sketch the "go to" copic marker, IMHO. The backgrounds around stamped images that I've seen folks make with these are just lovely, lovely, and I think using the airbrush to make patterned paper will rock!!
You can see some wonderful examples using copic markers at a lot of blogs including
www.debbiedesigns.typepad.com
www.ellenhutson.typepad.com
good luck