I don't know how valid this is but this article claims that 1366x768 is the most common screen resolution these days. It's aspect ratio is 16:9 so it's probably a lot of laptops that went from a 4:3 ratio (1024x768) to 16:9 and just widened the screen but kept the same height.
http://www.neowin.net/news/study-136…een-resolution