Many people have claimed to have seen this on a limited basis, but I have been seeing Ink on Google for a while today. I was first tipped off by my friend at Just Paper Roses.com. I have asked some other people and the switch appears to be only be seen by some.
People in the past have been happy with Google search (Google is one of the top brands in the world right now). With Yahoo branding the hell out of Yahoo search they want people to think Yahoo search. They do not want people thinking Inktomi or Google. It really would not make sense for them to announce a change. With Google's recent massive algorithm shift and upcomming IPO this would be a good time to switch search results.
Again, only some people are seeing the shift, but today is the first time I have. Time for me to tweak a few pages :)
Inktomi relies more heavily on page criteria vice links. The problem with really optimizing a page up for Inktomi is that one might trip the believed over optimization filter of Google. To give you an example of how easy it is to optimize for Inktomi take a look at this search for "website copywriters." Somewhere in the top few pages you will see my Website Copywriters on Search Marketing Info page which is rather short and has low link popularity.
There are a few techniques I would recommend:
1.) optimize the pages each for different terms by search engine. If one sold 5 HTP, they could optimize Inktomi for 5 HTP, and they could optimize the same page for 5 Hydroxytryptophan on Google. This should help you pick up traffic in the short term while you
2.) build a solid linking campaign which will eventually lift you in both engines for the desired terms
Some people may recommend making pages in two different versions (one for each engine), on a rare occasion I may try this. I do not recommend building an entire site this way though as it will make updating confusing. The end goal should be to generally have a strong enough link network that you can do well on both engines.