On Deb Ng's blog someone called me Susan, then quickly apologized (which I appreciated).
Susan is a perfectly good name -- if that's your name. But it isn't my name. I'm not overly fond of my real first name, so I only ever use it on formal documents that require my legal name, like W9s. The name I use in emails and on blog posts and as a by-line is the name I prefer to be called.
There seems to be a natural impulse among people to either lengthen a nickname or shorten a formal name, even with people we don't know. This is rude, no matter how you look at it. In a social setting, it might be easily brushed off. In a professional setting, it may cost you some work.
It's a matter of respect, really. When you decide to change the name of a person, it's a subtle sign that you don't respect them. You might think it is no big deal, but it is. Think about your own name -- why do you use it the way you do? Maybe another name has a bad memory, maybe you wanted to separate your adult self from your childhood self, maybe you just like the way your name sounds as is. Whatever it is, it is part of who you are. It's your identity.
As for me, my real name rhymed with my maiden name, which rhymed with way too many other words that led to a lot of childhood teasing. When people call me Susan, however, they don't realize the amount of pain that causes. It's why I cringe whenever someone calls me that.
Many years ago, I worked for a man named Don, who called me Susan two or three times before I summoned up the nerve to say, excuse me sir, but my name isn't Susan. He was pretty much a mean man, but for that moment he softened just a bit and said, "I know how you feel. My name isn't Donald. It's just plain old Don." About a week later, I saw plain old Don great a salesman who said, "Hello Donald, nice to meet you." Plain old Don said, "Meeting is over," and showed the salesman the door. As he returned to his office and looked at me and said, "If he can't get my name right, how can I expect him to get my order right."
If someone asked me for the best business advice I could give, it would be this: when someone introduces themself to you, call him or her by the name they give you. Always. It could be the difference between landing a great new client or having the door slammed in your face.