The NYT has a piece about email signoffs:  “Yours Truly,’ the E-Variations”.

 One point of contention is the significance of the closing “best”:

When Kim Bondy, a former CNN executive, e-mailed a suitor after a dinner date, she used one of her preferred closings: “Chat soon.” It was her way of saying, “The date went well, let’s do it again,” she said.  She may have been the only one who thought that. The return message closed with the dreaded “Best.” It left her feeling as though she had misread the evening. “I felt like, ‘Oh, that’s kind of formal. I don’t think he liked me,’ ” she said, laughing. “A chill came with the ‘Best.’ ” They have not gone out since.

“Best” does have its fans, especially in the workplace, where it can be an all-purpose step up in warmth from messages that end with no sign-off at all, just the sender coolly appending his or her name.

“I use ‘Best’ for all of my professional e-mails,” said Kelly Brady, a perky publicist in New York. “It’s friendly, quick and to the point.”

Lynn Gaertner-Johnston has this to say about “best”:

As for my preference regarding best as a complimentary close--I don't like it. Best what? When we mean "Best wishes" or "Best regards," let's use the whole phrase. When we mean "Best wishes for your recovery," let's say so.

In the body of a letter, we may write "Give my best to Mr. Washington." That's a complete thought whose meaning is "Convey my best wishes to Mr. Washington." But closing a letter with only Best feels incomplete.

Looking at standards in business letter writing, Best isn't among the standard complimentary closes, although the phrase "Best wishes" is.

Are you too busy to type your whole name?  Or are you so recognizable that everyone will know who you are by your initial.  

My thought is that if there’s one thing you generally do not want to convey to the recipient of a business email it’s that you don’t really have time to write the email and you are cutting corners for the sake of time.  The initial is an example of this, as are the dreaded all lower case emails and lack of punctuation.  My motto is, don’t send me one of those emails unless Exxon Valdez is running aground, you are watching it, and the email is part of your effort to prevent this from happening.  Where this is not the case, I will be slightly annoyed.