Would you go to trial without visual aids generated by Powerpoint or a similar program? If so, you should listen to John C. Dvorak's comments about speaking without visual aids on This Week in Tech #31.
Even though Dvorak wasn't talking specifically about lawyers and trials, he could have been. According to Dvorak, people have become so accustomed to having information presented to them visually that it is almost impossible to communicate with an audience by relying on your voice alone. Dvorak's own experiences in trying to speak without Powerpoint have taught him that "it just doesn't work." If you're going to try it, "you better be the best speaker in the world."
Dvorak's comments about Powerpoint take place about two-thirds of the way through the show, which also includes a discussion of some alternatives to Powerpoint.