From Science:
This column is intended for the edification of the uninitiated, those youngest science trainees who have not yet learned the truth about seminars and about so much else in scientific life — those who still think earning a Ph.D. takes only 4 years, that being 17th author on a paper is exciting, and that an experiment will work tomorrow simply because it worked today. In the idyllic vision of the uninitiated, a seminar tells a story, starting with a clear description of a problem, then outlining a series of steps taken to address that problem, and ending with a special reward: a glistening kernel of new knowledge. The speaker tells the story using vocabulary accessible to anyone with a similar breadth, though not necessarily depth, of scientific knowledge so that all in attendance can bask in the final, glorious revelation.
In reality, scientific seminars usually consist of quasi-related PowerPoint slides cobbled together from prior seminars and lab meetings, thoroughly and precariously dependent on an impossible quantity of specialized terms, assembled in a hotel room at 2:00 a.m. or covertly in the back of the lecture hall during the previous seminar. (At international meetings, I've often marveled at the number of speakers whose only audience members appear to be working on their own talks. It's like going to a restaurant and ordering lunch that you never eat because you're busy preparing dinner.)
More here.