If I recall correctly, Yahoo had a couple other offerings / search tools. They had something called YQL which you enabled you to treat a specific, public (supported) websites, like Craigslist for example, as a SQL table. SELECT * from <house_for_rent> etc, etc, etc.

I have no idea if this is what was used here but I know this is an example where I'm sure they didn't out source the search work to Google.