With dyslexia it can be very hard to spot spelling errors and misspellings, even when taking the time to re-read what you just typed. I can tell you it is very annoying and frustrating. Even more so when I know the word I wish to type but can't for the life of me work out how it is spelt. Sometimes I even have to reword a sentence to use a different word to avoid it!

And before you say "Google it" or "use a dictionary" that often doesn't work either as sometimes my "version" of a word is so far removed from the real spelling that spell checkers and Google have no idea what I'm trying to find.
One slightly unrelated thing that I do often is type the wrong word when speed/touch typing. The most common one being Think and Thing. Anyone know what the reason/cause of that is? As soon as I read back what I've written I always spot it.
I also sometimes type completely wrong, but correctly spelt words, if I'm typing fast and not looking at what I'm typing or the keyboard. Must be related to the other problem. Does that have a name, and a reason?
In regard to things like there, they're and their, I notice a lot of native English speakers get those and other examples wrong, and all that indicates is that they need a better education, or their schooling system failed them!
A lot of people also seem to have no idea how to use contractions, or for that matter what one is. Did you know that recent recommendations for teaching English was to remove the need for apostrophes from English? How would that improve anything.
The worst for me though is when people post in forums using txt speech. I want to throttle them! And if I get emails with txt speech I don't even bother to reply as the IQ level at the other end can't be too high.