The Asus UX31 ultrabook, which was just released, will come with a 1600x900 pixel 13.3-inch display but it is likely that the next generation of ultrabooks based on the forthcoming Ivy Bridge processors will come with a retina quality display, not unlike the iPad 2 and the iPhone 4S.
A retina display is one where the human eye apparently can't distinguish an individual pixel. Apple calculated that this was around 326 pixels per inch for the 3.5-inch iPhone 4 and according to Intel engineers, Ivy Bridge-based ultrabook will have displays of around 2560x1440 pixels, that's around 225 pixels per inch on a 13.3-inch display and probably closer to 250 ppi on a 11.6-inch model.
At 3.5 million pixels, these screens will almost certainly require a more powerful graphics subsystem in order to power them, which Intel is promising with the next generation Intel HD graphics.
In comparison, Apple's Macbook Air currently top 1366x768 and 1440x900 pixels respectively while most ultrabooks are unlikely to surpass a 1366x768 pixel resolution.
One of the reasons why Intel might be looking at upping the resolution for its Ultrabooks is to differentiate the segment from less premium products like bog-standard laptops and ultra thin netbooks.