I built my first kayak out of vacuum sandwich carbon-kevlar. It was finished since September 2009. Specifications comply: 10.2kg. It was my first time in kayak therefore few capsize later, I navigated on my first composit piece.
Later, I built an other kayak out of cavuum sandwich full carbon. It was finished since February 2010. It is just 7.6kg but it is very vulnerable to puncture.