I enjoy working with paper. My favorite notebooks are ISO A4 size because they give me a bit more vertical room and still fit well in my backpacks. The issues that come up with regard to US Letter size paper seem to be: 1) It's not metric -- yes that's true, but A4 is 210mm x 297mm. These numbers seem completely arbitrary and don't take advantage of the metric system. I wish the US was on the metric system, but it's…
However, there are some good ways to use 8.5 x 11 [2] that might look odd on narrower and taller paper.
[1] http://marginalrevolution.com/marginalrevolution/2012/09/why...
[2] http://retinart.net/graphic-design/secret-law-of-page-harmon...