I do it all the time in my own emails and even in some of my sales letters.
Sometimes my clients have even tested it and have seen this for themselves. The old school direct marketers did it all the time with HUGE success. And the reason why is because misspellings and bad grammar make you look more authentic.
Not perfectly formatting your emails, so some lines are longer and out of whack make it look like you wrote a personal, 1 on 1 email.
Using ugly courier font can sometimes (depending on the market) increase your response and (in email especially) make it look like you just dashed off a personal email or letter to someone.
This was just the case with an email I wrote last week.
It was not even on purpose, but it accidentally went out with really screwy format, one entire paragraph was twice as long as the rest of the email, clickthrus were through the roof (especially for a Friday).
It stands out in the inbox.
This is not
always the case. And I'm not saying to not use spellcheck. But sometimes purposely misspelling certain words will bring more "flavor" and personality to your communications.
And if it's done on accident, well, no big deal.
Sadly -- in America at least -- the majority of people read at less than an 6th grade level anyway. Most don't even know the difference between "their" and "there" or "its" and "it's".
I'm not even sure I do half the time
So I just don't worry about it.
Of course, if you are writing to a more sophisticated market who does care about such things (other writers, for example), then I would make sure every i is dotted and t crossed.
But for most markets (I've written for at least) not only do I not worry too much about my spelling, sales are often higher and clickthurs through the roof with an occasional misspelled word or out of place punctuation.
That's why I say it's worth testing.
Everything is worth testing, IMHO.
Even stuff I personally find annoying (
especially stuff I find annoying I like to test.)
Ben