Grammar, spelling - esoteric niceties or compelling necessities?

In on-line communications (e-mail, blogs, tweets certainly!), syntax and punctuation have already fallen by the wayside, but how about grammar and spelling? Do they still matter?

Frankly, when I receive an e-mail that starts with "Hey their", my finger is on the "delete" key in a split second. Am I missing an important business opportunity because I cannot get past that "Hey their"? Or how can I keep from feeling less positive than before about the blogger who habitually writes "it's" instead of "its" -- as in 'the house and its rooms', 'the proposal and its goals' - or uses 'criteria' when it should be 'criterion'?

So, this is my question today: do grammar and spelling still matter or have they become esoteric niceties?