I remember back when Yahoo bought AlltheWeb. Most Webmasters and SEOs were a bit upset, because AlltheWeb was one of those upcoming search engines who really could compete with Google back in the day.
So Yahoo acquired it back in 2004 when Overture, which acquired AlltheWeb in 2003, was acquired by Yahoo. Very early 2004, Yahoo was shopping for search engines to buy, so they no longer have to be dependent on Google's search engine. They were expected to use Inktomi which they acquired earlier, but then they bought AllTheWeb and Alta Vista. They made changed to both engines and released their own flavor of Yahoo Search soon after, surprising some webmasters.
AlltheWeb had one of the largest web indexes back then and was loved by Webmasters.
Now, well, those investments are gone. They outsource their search technology to Microsoft and will redirect the technologies they acquired in 2004 to Yahoo Search, which is powered by Microsoft.
The funny thing, they are doing this on Microsoft's birthday - April 4th!
Forum discussion at WebmasterWorld.