I'm not saying one's better than the other, Si asked what Americans use...
I'm not saying one's better than or easier to use than the other... Si asked what units should be used for a book aimed at an American audience. Now, EVERYBODY in this thread has said to some extent that Americans are silly for sticking with Imperial (I've always heard it called American Standard) units instead of embracing Metric.
What I'm saying is a book aimed at Americans would probably benefit from having its measurements in American Standard, or Imperial Units.
Again, I'm NOT getting into a debate about which is better or easier or anything like that. I'm merely answering the question that was asked in the very first post of this thread. This isn't a you're wrong, I'm right deal... it's what's better for the target audience.
For example, if I go out to my wood shop (garage) right now... my table saw, framing square, combination square, tape measure, etc are all in American Standard. I searched my entire house for anything with Metric on it... I found one six inch ruler with metric on the other side.
I'd hazard a guess that's why we never switched over. It would cost a ridiculous amount of money to convert all the tooling over from American Standard to Metric. I'm guessing it's a cost/gain problem, not an unwillingness to learn.
Again, not picking a fight. Not trying to label myself the, "Crazy love of country, American Standard or GTFO," guy. Just saying Americans use American Standard so it makes sense that I book aimed at Americans uses American Standard. One book isn't going to convert an entire country over to Metric.