"eBay was set on Monday to make access to its application programming interfaces (APIs) free to its more than 21,000 developers for creating programs that enable people to buy and sell things through the online auctioneer's network. Previously, developers paid from $1.25 to $2.90 per 1,000 items listed and an annual fee of $500. eBay also is sponsoring a developer contest with a top prize award of $5,000 for the most innovative application."
This is a common sense move in the Web 2.0 world, because it no longer matters if users buy and sell on eBay's official website. As long as eBay gets a cut of the auction, the User Interface could be in Timbuktu for all they care. To paraphrase Steve Ballmer, it's all about Data, Data, Data (cut to monkey dance).