This also came up on either a BBC or CBC science program, but not as a linguistically-oriented discussion.
Over the last two or three years I've noticed a lot more people starting a sentence with "so": "so when we take the ...", "so I have this ...", "so the basic idea ..." and (uh) so on.
What is "so" when a sentence begins with it? When did it start? Is it just a "pause" word (and is there a word for that)? Is it grammatically correct? Am I the only one that finds it annoying?
Edit: Much of its usage in scientific discussions is as a "therefore".