Ever wondered how big the fictional continents of Westeros and Essos are compared to the real-life USA and UK? No? Well, disregard then. For those who have, this is a (very) rough image I knocked up to show the comparison:
Some interesting points: Skagos is the same size as Ireland, so not the tiny little island readers may be expecting from its size on the map. And Dany's journey in A Game of Thrones alone (not to mention the north-west length of Westeros) spans a greater distance than the east-west width of the United States. Also, the North is so huge it can swallow up the entire British Isles several times with room left over. And Catelyn's travels in A Clash of Kings were the equivalent of crossing Texas and back again with surprisingly little trouble.