I don't know why we need so large graphs but the interesting thing is that we have also the graph of the Internet. Can you imagine the number of nodes? Even more interesting some people are tried to visualize these graphs.
You really need a good computation power or you need to model abstraction of the whole graph. Luckily, we have some graph clustering methods and we are able to manipulate visual clues, using the current research.
One sample graph can be found here.