One of the early histories of Saturday Night Live talked about the first meeting of the writers. Even though they had never met one another, and were from different parts of the country, they had a common language and thought that the same kind of things were funny. It was compared to jazz musicians, who can jam with one another even if they've never met, because they share the same vocabulary (and, dare I say, are familiar with the same problem domain).
The same thing happened last weekend at No Fluff, Just Stuff in Orlando. One of the speakers became ill at the last minute, and the organizer had to scramble to find speakers to fill his spots. I filled one of the talks, about fallicies in enterprise architecture, after never having seen the talk and having a whole 10 minutes to look at the slides for the first time. However, the talk came off really well -- I managed to talk for the entire ninety minutes, and got good scores. Because the problem domain was familiar, I was able to extemporize the talk, bringing my own experience to bear. This talk wasn't about tools or APIs, but about common fallacies developers face in enterprise situations. Well, I've seen a lot of that. Of course, I'm sure my rendering of the talk is no where nearly as good as the original and that the stories and experiences I bring are completely different from the original speaker. However, it reminded me of a jazz trumpet player showing up to a gig and saying "'Girl from Ipanema', extra solo after the chorus, and watch me for the finish. A-one, and-a Two, and...".