I like this article as an excellent behind-the-scenes of all the prep work that goes into a talk.

That said, one key element is missing: the enthusiasm/delivery of the talk itself. What I mean is it's not enough to know the talk -- you also have to "know" the enthusiasm.

Personally, I think this is the hardest part, because enthusiasm is usually built up between people (as in you are talking to a friend, they get more excited, so do you, and each feeds off the other). When you present, there is no "other person" to feed off of, meaning you have to create that mood all by yourself. Presenters who do this are very desirable to listen to, regardless of what they're presenting.