Google/Ebay

eBay has consistently been one of Google’s largest customers, accounting for perhaps 2% of Google’s gross revenue and profits in 2006.
Google has been one of eBay’s largest provider of leads, currently accounting for 5% of its traffic, but a smaller percentage of its revenue and profits
Several 'Power Users' at the eBay event said their interest and their traffic dropped dramatically after their keywords were pulled from Google, so clearly there is a greater risk to eBay