Feeling for the guys who started IndexTank replacements and other Search-aaS companies. Infrastructure is a poor place to be with AWS around. Just a matter of time until they offer every low level service.
They can have one advantage over AWS: customer service. That's what made IndexTank, we would have never made it as user-friendly without our close relationship with our users.
Not just customer service, too, but end to end developer experience can be a huge advantage. I'm personally very active in maintaining the popular Sunspot Ruby library for Solr, and have passing familiarity with the internals of half a dozen other clients as well. This makes for improvements at all levels of the stack.
While the CloudSearch API looks a bit more reasonable than the recently released DynamoDB, Amazon has traditionally been somewhat poor in terms of end-to-end developer experience.