I was looking at my list of YC acquisitions earlier and noticed an interesting fact: Yahoo! has never accquired a single Y Combinator startup, either for talent or technology ( http://ycuniverse.com/ycombinator-companies.php?status=acquired ).
One interesting note about that fact is that Yahoo! was the purchaser of Viaweb back in 1999, which formed the genesis of Y Combinator itself.
Another interesting detail about Yahoo!'s lack of start-up acquisitions is that Yahoo! CEO Marissa Mayer has stated she may not return the cash from selling Alibaba to Yahoo! shareholders, which may signal a very positive and healthy buying spree by Yahoo! for talent and technology in the near future.