While browsing around at Presentation Zen I came across Living large: “Takahashi Method” uses king-sized text as a visual.

Takahashi uses only text in his slides. But not just any text — really big text. Huge text. Characters of impressive proportion which rarely number more than ten, usually fewer. The goal, he says, is to use short words rather than long, complicated words and phrases.

I can see a point in using text only since images might distract the audience. Keeping the text short, easy to read and easy to remember is also a good idea.