A friend of mine was asking about this today, but was saying it was the paid service being shutdown, so effectively they won't be able to stop ads being shown on their corporate website.
Not really sure what the alternatives are.
We have actually converted quite a few Google Site Search customers over (lack of customizations, lack of phone support etc.) - www.cludo.com
The weird thing is that lack of time you get to find an alternative, it doesn't put Google in a good light.