I've done a bit of carpentry around my house. Since I live in Sweden I always use the metric system.
For me the focus on division by three is a bit strange. Sure I sometimes need to divide by three, but I also need to divide by five, or two or seven. I guess the thing is that our building standards are expressed in the metric system, so it makes sense thinking about them in terms of meters or centimeters. US building standards are expressed in the imperial system, so it makes sense to think about them in feet and inches.
Why would I want a unit that's 1/60th of a meter when I have a perfect 1/100th of a meter? A third of a meter is 33.3cm, working with wood you don't need more precision than that, if the decimal sign makes it difficult to do calculations, just step it up to 333mm.
I'm not a carpenter by trade but I guess that a professional carpenter here learns quite well how to divide by three even in metric. I see this argument popup every time there's a discussion about using the metric system in the US and I find it weak. For me this argument only sounds like "but it's hard to learn something new".
I'm sure there are pros and cons with both the metric and the imperial system, but in the globalized world we live in, the fact that The Rest Of The World uses the metric system should be a pretty convincing argument to use it in the US as well. I mean after all, The Rest Of The World has accepted English (in one form or the other) as the Lingua Franca in order to make communication across borders easier. You don't see us whine about stuff like "but in Swedish I can much more succinctly express that it's my paternal or maternal grandparent I'm talking about, so I don't want to use English".