If I know someone has seen my name spelled a few times, but likely didn't have the spelling to hand when writing to me, I might be a little miffed at a misspelling, but understanding.
However! When someone is replying to an email I sent from work (in which I KNOW they have my first name spelled correctly right in front of them SEVERAL TIMES) and this someone has corresponded with me for the last TWO MONTHS, I think I am allowed to be a bit testy when they address me as 'Kerry'.
I am sure it was a perfectly innocent bit of thoughtlessness, but it did elicit the snarky thought: I realize my parents were being rather cutsie when they named me, but, if anyone is going to 'correct' their faux pas, I am quite sure that person should be me.
At least I have a well-developed sense of wry humor. :p