When you always outperform, investors always expect you to outperform. And when you disappoint, investors are going to be extra disappointed.

After the bell yesterday, eBay (NASDAQ:EBAY) reported fourth-quarter earnings and came up a tad short of expectations. The online auction giant saw fourth-quarter revenues jump a healthy 44% to $935.8 million, driving net income growth of 44% to $205.4 million, or $0.30 per share. On a pro forma basis, the company earned $0.33 per share -- a penny short of the analyst estimate.

The company's outlook was also light. eBay forecast first-quarter earnings before items of $0.34 to $0.35 per share on revenues of $1.01 billion to $1.03 billion, well short of the analyst estimate for earnings of $0.40 per share on $1.05 billion in revenues. The company also said that it expected fiscal 2005 earnings of $1.48 to $1.52 per share on revenues of $4.25 billion to $4.35 billion. That, too, is short of the analyst estimate of $1.61 in earnings for the year on $4.37 billion in revenues.

As a result, eBay shares traded down nearly 18% to around $85 a share in today's trading.

Though the numbers didn't quite make expectations, the business is still growing rapidly. eBay's international business led the way, with net transaction revenues surging 64% to $344.3 million -- almost matching the $362.7 million in net transaction revenues the company recorded in the U.S. Meanwhile, the PayPal payments business posted net transaction revenue growth of 53% to $200.2 million.

Total gross merchandise volume (GMV), the value of the items successfully traded on eBay, rose 39% to $9.8 billion during the quarter. eBay Motors, by far eBay's largest trading category (as we discussed a couple of months ago in "Investing in Car Culture"), continued to outpace overall growth, with annualized GMV climbing 48% to $11.1 billion.

At 60 times 2005 earnings, eBay's stock still carries a premium valuation. That said, there isn't much wrong with the actual business. Last week, the company announced a hike in its listing fees (see "eBay, Hike, and Other 4-Letter Words"), hoping to capitalize on its network advantage over auction competitors such as Yahoo! (NASDAQ:YHOO), Amazon.com (NASDAQ:AMZN), and upstart Overstock.com (NASDAQ:OSTK).

Yesterday, eBay also announced a two-for-one stock split, payable Feb. 16.

eBay and Amazon.com are both Motley Fool Stock Advisor recommendations. Overstock.com is a Motley Fool Rule Breakers recommendation.

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Fool contributor Jeff Hwang owns shares of both eBay and Overstock.com.