GitHub User: agh
It is not hard to make chef-server run redundantly.
A decent number of large users are not using chef-solo and there are definitely approaches that you can take to resiliency with the chef-server infrastructure.
Obviously Engine Yard is one of the poster children of chef-solo but last time I spoke to anyone from over there, they are also still on 0.6.x whereas the rest of the world has largely moved onto much newer releases. They're probably not the best example of a "large scale" user unless your needs marry closely with what they wanted.
Speaking personally, the benefits provided by Search are more than worth any hassle involved in making sure the API calls always get answered!