Apparently Microsoft might be buying Yahoo, a move that would have quite a big effect on SEO.
If the deal goes through then Microsoft is likely to pool the search algorithms and create something that can really rival Google. They would have a ready made market share and could pose a threat over the long term. In the UK I don’t think anybody would notice because Google is too far ahead but in the US the effect would be much larger.
One alternative theory is that Google will take over Yahoo, they are cash rich and wouldn’t want their dominant position to the threatened. I think if Google can make the deal they should grab the chance with both hands.