Since I am also a Sharpie-aholic, I went ahead and bought a set at the office store to try out.
Overall it's a disappointment. The pen[cil] does not write smoothly, more like a cheap ballpoint. When you do write with it, it leaves a relatively deep impression in the paper that makes it virtually impossible to erase completely. At the same time, the "liquid graphite" is very easy to smear, or "erase" with your finger or hand.
The uneven quality means that it is not any good at the things I love doing with a pencil- shading, varying stroke weight, messing around. I'm really not sure that it is good at anything. I will check it out to see how permanent it is tomorrow.
Guess I'm stuck with my mechanical pencil fallbacks, and all my Sharpie pens (which I heart) and markers.