When to definitely use SOLR over Lucene in a Sitecore 7 build?

Question

My client does not have the budget to setup and maintain a SOLR server to use in their production environment. If I understand the Sitecore 7 Content Search API correctly, it i

Answer 1

Stephen pretty much covered the question - but I just wanted to add another scenario. You need to take into account the server setup in your production environment. If you are going to be using multiple content delivery servers behind a load balancer I would consider Solr from the start, as trying to make sure that the Lucene index on each delivery server is synchronized 100% of the time can be painful.