I found an article called "WMAP Cold Spot Extragalactic Radio Sources." I'm having trouble providing links (don't ask), but you can Google the title directly. The article examines various possible explanations for the cold spot, and cites a large void as one of them. How large would the void have to be? They calculate that for 0.5<z<1 the void would have to be on the order of 280 Mpc (913 million light years). They calculate the probability of finding a 280 Mpc void as 5x10^-10. Bet they never thought that horse would pay off.