Hi,
Here are some thoughts based on being a technology trainer while employed as a reference librarian and then while working at/hiring at the Gates Foundation's US Library program.
I cannot say enough good things about the power of team teaching. I know it is not always possible, but when it is, I highly recommend it. If you can find two people with complementary skills (one is more "techie"; one is more "soft"), those classes can be beautiful. You learn so much when you see how different people approach the same topics.
I think there's a tendency for people to think that the trainer needs to be totally technically oriented, but many of the best trainers are more in the middle -- they understand and like the technology, but can also empathize with where the novice is coming from. Knowing how to use a tool and knowing how to teach it are such different things.
I think reference librarians often make good trainers, because they have watched so many people interact with the tools and they are aware of the questions and confusions that frequently come up.
No matter who teaches the classes, I think an interactive format makes all the difference. One of my favorite books for people doing technology training is "The Complete Computer Trainer" by Paul Clothier. It's an oldie but a goodie.
Wow! This post is long -- sorry to have rambled, but I like this topic
Brenda