I don't worry about NaCI itself, I worry about someone who's too stupid to implement it correctly. And those people are everywhere, especially in big companies. i.e. Nintendo, broken (self built!) RSA in the Wii or even better Sony, using the same "random" number for all their crypto on the PS3... yes FX and Chrome are Open Source, but MS and Opera are not.

Anyways, I'd rather spent a lot of time improving the JITs instead of writing "optimized" low level code myself these days.