Remember the advertising-laden skyscrapers from Blade Runner? Mitsubishi's now got the tech to do it: its Diamond Vision screen uses individual 4-inch square OLED panels that can scale to an unlimited size. Check out the 155-incher on show at CEATEC:
That's definitely the biggest OLED screen I've heard of. Of course, the individual panels are a bit of a cheat—and mean you only see a red, green and blue matrix until you're at least 2 feet away—but Mitsubishi imagines the tech being curved around buildings, trains and buses in Japan.
OLED screens are capable of much higher resolutions than regular stadium-style LED displays, but have two fatal flaws. They're super expensive, and OLED degrades. The expected life of an OLED panel is only about 20,000 hours (roughly 2.5 years for a 24/7 advertisement). Gorgeous as they are, that expense is why you're not reading this on an OLED screen right now. [OLED-Display.Net and Network World]