I complained the other day on Twitter about Courier font. Here's my problem with Courier: Aside from being rather ugly (to me), it is wide as hell. So using it adds A TON of pages. I have very little time. When I see a manuscript to read/edit that is 400 pages long, I grumble to myself, because it might take me forever.
But when that same manuscript is put into Times New Roman font -- HOLY CALIBRI! -- it is only 315 pages! Highly manageable!
Obviously the number of words and the order they are in has remained the same. I recognize the fact that I will read these two manuscripts in approximately the same amount of time whichever font they are in. I know that if I cut the ms down to 4 point font and removed the spaces, I could probably fit it onto a set of index cards and that wouldn't make it faster to read either. I KNOW. But so what, it's my alternate reality, let me live in it.
ANYWAY. This tweet caused a bit of a furor. Authors everywhere chimed in, agonizing that this or that teacher or book told them they must ALWAYS use Courier, and now I'll hate their manuscript, etc etc.
You are overthinking it.
My first encounter with your work is in an email. I assume that you (like most people) are using one of the generic email fonts, either sans serif or serif, and either way, it's no biggie. I don't expect emails to be double-spaced (though if they are, I won't get mad or anything) -- it's an email. I know formatting often gets lost.
If I request a manuscript, I just want it to be clean and readable, like at school: Your info on the first page. (Where on the first page? Don't care.) 12-point-ish simple, professional, legible font. (I prefer a serif font such as TNR because it is easier to read for long periods of time than sans serif like Arial, but I am not going to get mad about it). Pages numbered. (Which corner? Don't care). Double spaced.
I truly cannot imagine a world in which the choice of font, provided it is fairly generic, curlicue-free, normal and readable, would impact my enjoyment of a great manuscript. If for some reason I am mortally offended by your choice of font, it is the work of a moment for me to change it myself.
Hound of the Baskerville, isn't there enough to worry about without adding to the list?