You know, like "hello" or "hey"...?
Let me tell you, it drives me banana-freakin'-sandwich every time I hear someone say that to me because, I will have undoubtedly started to tell them about how slow work was, or how I'm super bummed 'cause I just finished the last episode of Psych season 4...and I'll look up and they are gone!
Suddenly I feel betrayed, used...like they never actually wanted to know how I was doing!
I feel like I should run after them, haul them back to my work station and make them sit as they get just what they initially asked for!
Using "how are you doing?" as a greeting is like saying; "how was that weekend in Chicago?" or "tell me about the rest of Psych season 4, I know you just finished it!"
Both require more explanation and if they are used as a simple greeting they leave the recipient hanging; much like the way Psych season 4 ended...
(By the way, if you've noticed that I'm on a Psych kick it's because it's practically my new favorite show, and I would highly recommended it as it is very entertaining.)
Bottom line is...
If you are going to use a greeting, use a proper one. Don't just substitute any random sentence that requires more than two words to answer. You may just get what you ask for.