I'm feeling adventerous enough to take my best shot at this one...
Graphite is cool stuff. The way those carbon atoms have bonded to form graphite works wonders at doing stuff like lubricating the axles of my kids pinewood derby racers. It makes it so those wheels spin nicely. However, the resistance of fluid flowing by a kayak is VERY different than friction of two solid surfaces sliding. The two situations are fundamentally different, kinda like night and day different. In the fluid flow situation you are dealing with phenomona like laminar flow, turblent flow, boundary layers, wave making -- with controlling parameters like viscousity. It has been a few years since my fluid dynamics course work, but it was fun stuff to play with.
I have heard that a finely polished hull could move through the water with less resistance than rough scratched hull. Sailboat racers have been known to spend many long hours smoothing their hulls -- makes sense to me. I'd love to see come controlled experiments done to quantify the difference between a smooth and scratched kayak hull. It'd also be interesting for the sake of this discussion to add graphite / non-graphite controls to the experiment. But, like Brian, I am more than skeptical concerning attributing speed gains to graphite in the epoxy on one's hull (unless one is also sliding the boat over rocks as part of the speed trials, in which case I could acknowledge graphite as possibly decreasing frictional resistance).

-John D.

: You probably don't feel like explaining, but I'm gonna ask anyway hoping I
: might learn something. Why?