The Samsung Galaxy Tab, unlike its Galaxy S phone little brothers, uses an LCD display instead of the company's wonderful Super AMOLED display.
Of course, making one that's 4-inches is quite a different ordeal than making one that's 7-inches. Production cost reasons kept the AMOLED technology out of the Galaxy Tab, but you can bet that a future model down the road will have it.
A good indication of this is that Samsung will display a 7-inch WXVGA (1200x600) resolution OLED screen at an exhibition in Japan running next week.
Production of this panel will start in June 2011 and Samsung plans to sell this panel in the very same year. Not only that, but Samsung will be selling the panel to other companies, so we could see competing tablets running OLED too.