Google's latest Webmaster Help video discusses Google's need for text in indexing content. Matt Cutts responds to a question about how important text is in getting Google to understand their site. The user has a site that is mostly made up of images, and says that users like it better, bounce rate has declined, and conversions are up.
"Google does still want text," he says. "So there's a couple options. One is: if you have an image that you've made of some text that's really beautiful, you can include some textual content there. You can sort of say, 'alt,' you know, or the title - that sort of thing. So you can say, for an image, here's some text to go along with that, and that can help."
He goes on to say that one reason a site might be having more user interaction, time on site, conversions, etc., is because it's prettier. "And we see that," he says. "Better design can help people enjoy and use your site more."
He also suggests considering Google Web Fonts.