There were 588 million new listings added to eBay worldwide in Q1-07. At any given time, there are approximately 100 million listings worldwide, and approximately 6.4 million listings are added per day. eBay users trade in more than 50,000 categories.

eBay has 233 million registered users worldwide. 

If eBay were a country, it would be the 5th most populous country in the world behind China, India, the U.S. and Indonesia. (Source: U.S. Census Bureau, International Data Base, April 2005)

More eBay facts here.