I'm subscribed to a few of the official Android mailing lists, and one message came along today that got my attention - a link to a New York Times article on how touch screen phones can help blind people using the G1 as an example. Some excerpts:

Since he cannot precisely hit a button on a touch screen, Mr. Raman created a dialer that works based on relative positions. It interprets any place where he first touches the screen as a 5, the center of a regular telephone dial pad. To dial any other number, he simply slides his finger in its direction - up and to the left for 1, down and to the right for 9, and so on. If he makes a mistake, he can erase a digit simply by shaking the phone, which can detect motion.

Now that is brilliant - software that centers its UI wherever you first touch. Hell, I could see that being useful even for sighted people, like a stereo remote control app - just pick up the phone and start jamming with your thumb and it'll do what you want. And for the future:

"How much of a leap of faith does it take for you to realize that your phone could say, 'Walk straight and within 200 feet you'll get to the intersection of X and Y,'" Mr. Raman said. "This is entirely doable."

The article makes a good point, that it's not just enough for software to read the text off signs; the problem is that the blind won't know where the signs are to begin with. Maybe that's the sort of thing that a massive, free map/geoinformation system like OpenStreetMap would be good for helping, by including a sign layer. Or maybe you could just have a huge camera on your chest.