I just can't bring myself to do it. Almost everyone who send me emails starts them, "Hi" and although it doesn't grate on me, it's not something I can bring myself to do. Which - I have to admit - is just a little odd as I have no difficulty in ending my emails "Regards" - or even, sometimes, "Kind regards".
Language, I am very well aware, is a living thing; it moves, it changes, it develops. And that is how it should be. After all, Old Bill the Bard is venerated for having introduced (or even invented) goodness knows how many words. Infinitives I can split with the next man, despite knowing that a split infinitive is a grammatic abhorrence - but there are times when sandwiching the adverb just seems to give it a bit more punch. As in "to boldly go", for example.
Back in the day, I was firmly instructed (or instructed firmly) that business correspondence opened "Dear Sir" and closed "Yours faithfully". If one was well acquainted with the correspondent, the salutation could be the less formal "Dear Mr Smith", in which case the closing would change to "Yours sincerely". Of course, letters to family and close friends would open with "Dear Jim" and close with "Love from". There would then be numerous permutations of opening with things like "Dear Prime Minister" and ending the letter of resignation with "Yours truly" or even "Yours ever" - although both the salutation and either closing would perhaps be somewhat tongue in cheek.
Of course, we have all seen examples of letters from the first World War trenches ending along the lines of, "from your affectionate son, Jack" - which simply goes to prove my point about language being a changeable commodity. but I still can't open an email with the word "Hi".