My train of thoughts:

> Everyone who applies for a position at either of my companies, iFixit or Dozuki, takes a mandatory grammar test.

Whoa. Who do you think you are - google? What makes you think I am going to sit through your grammar test? If I am agreeing to your grammar test, either you are one of the most desirable places to work for(never heard of you), or economy is about to collapse and this is the only job I can find, or I am so incompetent and/or desperate that I will take anything that comes my way(beggars, choosers etc).

> Of course, we write for a living.

Oh, should have mentioned it earlier. I won't have gone into internal monologue.

> But grammar is relevant for all companies.

May be it is. But not as relevant as you make out to be.

> In blog posts, on Facebook statuses, in e-mails, and on company websites, your words are all you have.

Apart from my words, I have my intent, thoughts, opinions, facts. Words are a medium. You are giving them undue importance. If I am reading an article about face recognition using opencv, I am interested in code snippets and concepts. My mind auto-correct "there, their, they're" or "its, it's". If I am reading about "infant mortality rate in India", I am interested in figures, reasons, solutions. That is not to say grammar or writing style doesn't matter. I am saying it's not as important as you put it to be, and good writing doesn't automatically come with proper grammar.

> If it takes someone more than 20 years to notice how to properly use "it's," then that's not a learning curve I'm comfortable with.

You are assuming someone good at something is assigning equal amount of weight and is equally interested in grammar as he is in whatever he is good at. I know good programmers who write weird English. Anecdote, data etc. Neither of us have data, anecdotes don't count for much.

> So, even in this hyper-competitive market, I will pass on a great programmer who cannot write.

Don't worry about it. To pass on a great programmer, you will have to get them interested in you first. It's a win-win situation. They aren't going to flock to your offices to take your grammar test, and you won't have to pass on great programmers due to bad grammar.

> Grammar signifies more than just a person's ability to remember high school English. I've found that people who make fewer mistakes on a grammar test also make fewer mistakes when they are doing something completely unrelated to writing — like stocking shelves or labeling parts.

Citations please. Also, unless you are stocking shelves, how does it matter? Never came across a programmer whose desk is always messy(I never came across one whose desk is clean)?

> In the same vein, programmers who pay attention to how they construct written language also tend to pay a lot more attention to how they code.

Citation please. And how do you know it's not the other way round?

> And I guarantee that even if other companies aren't issuing grammar tests, they pay attention to sloppy mistakes on résumés. After all, sloppy is as sloppy does.

I am all for proof reading resumes and cover letters, but "sloppy is as sloppy does" assumes someone who is sloppy at something is sloppy at everything. That's as far from the truth as it can be.

> Grammar is my litmus test.

You must be fun to work with. A CEO whose litmus test to hir a programmer isn't programming finesse or cultural fit or drive..., but how good is his grammar.