Kevlar canoes (made in the same style/process) aren't significantly heavier than carbon (a pound or two spread over a tandem), but carbon is stiffer and in many ways more durable (less subject to uv degradation and water infiltration). I'm hoping to score a Savage River Blackwater as soon as I can rope the money- They make beautiful canoes from superb designs.

As for conductivity carbon fiber is a conductor, albeit a relatively weak one. The level of conductivity is great enough that bicycle (and to some extent canoe) fabricators run the risk of galvanic reaction between metals causing corrosion. As for lightening.... I hear that Muck boots make you immune.