Hah! This Ask Yahoo question (Why do most UFO sightings happen in the United States?) popped up on my Gmail Clips this morning which I found completely fascinating! Particularly this paragraph:
The National UFO Reporting Center lists thousands of "close encounters" submitted by users. According to its database, the United States has far and away the most reported UFO sightings. In fact, California alone has reported more than China, England, India, and Brazil combined.