My interest in graphics lead me to be very curious about Eco-font when I read about it on the TED blog late last year. Ecofont is designed to cut ink use; the main website claims it can be 20% less.
When I first downloaded and tried it, I was disappointed. It renders very badly on a computer screen, and looks relentlessly washed out and gray. I recently changed my mind, however, when I saw it actually printed. Using a standard inkjet printer and regular font sizes (11 or 12 point), it is quite readable, much more so than on the screen. At larger sizes, however, the ink-saving holes become more visible and legibility starts to become an issue again.
I’m not using it for things that will probably remain digital (manuscripts that will be sent by email, etc.). I do plan on using it for forms and things that I have to print.