I did the hybrid spelling thing for my book (and make note of it on the copyright page at the bottom) because the whole convention is a
clusterfrog. (That's right, I said
"frog"—so cancel me!) But seriously, I realize that to people in the UK, my book will look like it's full of spelling errors if it uses US spelling, and vice versa. It was this lose/lose spelling proposition that made me say
frog it. ["Look Mildred, there he goes again!"]
P.S. In all of this back and forthalizing (z? or s? pick your country), we can lose track of the fact that publishing companies seem to make their own rules anyway. Some follow Strunk. Others AP. Others, Terence McKenna's School of Mushrooms.
It's like the space around em dashes: it's appropriate for journalism (papers, etc.) so why not in books? Seems like such an arbitrary, wonky law. It's not like it can be lawfully justified; it's just a stylistic/visual preference.
When I look at space around an em dash I think "Wow, it looks more open and truly conveys some kind of a separate thought from the main theme." whereas others go "Ewww!"
And then I think of readers. I hope they can get past all of this
frogging ship about writing technique and actually get something from the words themselves. If they can't, then they're probably not going to absorb my material anyway.