There are so many I quit trying to remember the ones I've seen. Careless use of apostrophes is rampant...but it's hard to tell which are ONLY careless due to hurried typing and which are the result of flatly not understanding the use & rules.

There are other 'little' things about which many people just never bother to even learn the correct usage...

Grammar usually refers to word order and proper use of modifiers and constructing a sentence so that infinitives are not split, but punctuation and spelling are much easier to notice.

Oh...one that really gets me is the way a large portion of the military doesn't know the difference between a 'contingency' and a 'contingent'.

I know that misusing 'there' 'their' and 'they're' is mostly a spelling issue, but continued misuse seems to me to indicate a general vagueness about their place in the language. This is a bit like Ebbie's example. In these days of the WWW (World Wide Web..not 'internet' in most cases) the word site is used/spelled as 'cite' or 'sight' all too often.