Hmm …

… Anecdotal Evidence: `What's It Look Like?'

A more recent popularization of the word is utterly repellent. People, often strangers, begin emails not with “Dear Patrick” or even just “Patrick” but with “Hi Patrick,” omitting the comma separating the noun of direct address from the rest of the sentence. This is marginal literacy masking as informality and friendliness. 

Had I, in an email, addressed a colleague "Hi, So-and-So," said colleague, I suspect, would have thought the comma precious. An email is not a letter, actually, though you are free to pretend it is one. Still, I am prepared to apologize to all and sundry for my inadvertent utilitarian rudeness.