Stock market investors are a funny bunch... eBay decides to buy Shopping.com for $620M. Investors don't like it (okay, that's fine), but because of that, eBay's market cap (based on stock price) lost $2.5B. So in the short term, the acquisition of Shopping.com really costs eBay $3.2B.
Of course, the price will recover, but it's interesting nonetheless. Might not be a bad time to snap up some eBay stock.