This expression is in reference to the (former) largest oil spill in North American history when the Exxon Valdez tanker spilled 10.8 million gallons of unrefined Alaskan crude oil into Prince William Sound. (The Gulf disaster has far eclipsed that number, spilling an estimated 108 million gallons as of July, 2010.)
AOL's data Valdez released a total of 36,389,629 individual searches. They intended the files to be an academic resource but didn't consider that users might be upset to see their private queries become a research tool.
Click on "more info" below to see "The 7 Ways People Search the Web according to AOL's users."
NetLingo Classification: Online Jargon