My dad wasn't a big fan of hemlock, back when he ran the family portable sawmill business. I assume he was referring to the eastern variety. Knots, heavy, brittle... likes to split and shatter rather than give a bit. If I remember him correctly, he thought it'd be fine to use for cheap studs in a barn or what not, but for any other purpose, he'd rather some other wood. I figure he'd say the same for use in a kayak.

I think the poison hemlock is another plant... Wikipedia thinks so, too: http://en.wikipedia.org/wiki/Conium ; http://en.wikipedia.org/wiki/Water_Hemlock . Otherwise, I can only imagine what my dad would've thought of it ;o)