One of my pet peeves is when people arbitrarily start sentences with "so" when they are not transitioning from anything, particularly when I see/hear people answering questions and starting their answer with "so" for no reason. It drives me batty. An example...

Question: How many years have you been studying this phenomena?

Answer: So, I've been studying it for a long time, almost a decade.

I noticed it was more often scientific or economic or technological experts doing it, and it always comes across to me as a nervous tic, and it makes these experts seem less confident about what they're saying, to me anyway. The usages that don't bother me are when someone's getting ready to tell a story or share a personal anecdote like, "So there was this girl at the coffee shop, right?" or ask a question like, "So where are we going tonight?" Both are still technically wrong, but they don't come across as a bad habit or nervous tic, as a replacement for "um" or "uh" as it does in other cases.

I decided to Google "starting a sentence with so" and found a lot of discussion on the subject. There was one blog entry that made a lot of sense of it, even if it didn't quell my annoyance...

Set-up: How do you know that your son will grow up to be a scientist?

Punch-line: His first word is "So ..."

The joke here, of course, is that quite a lot of scientists seem to always begin speaking with the word "So." And not when they're giving the conclusions to an argument — they aren't using it to mean "therefore."

They just start from a dead stop with "So ... ". They seem to use it the way non-scientists might begin with "Um" or "Well". (I've heard computer professionals use "So", but I hear this as an attempt to sound more scientific.)
Because it makes so little sense, The Scientist So reminds me that science is a subculture. Subcultures do develop funny tics that seem to have no practical purpose — handshakes or dreadlocks or backward baseball caps. Although such tics seem to simply exist to exist, they provide a way to identify and control membership in the group. They do a job, whether they make any sense in themselves or not. Maybe The Scientist So marks the speaker with a cultural affiliation — that of "Scientist."
[Full Article: Scientists Say So]

Wise, do you hear this often with your colleagues?