This tightly couples Sphinx to your application and your schema, and creates serious issues for your ops team since every app change potentially needs to modify the Sphinx config. It gets particularly hairy when you want to host multiple applications using a single Sphinx daemon.

We started out with Sphinx for our apps but quickly discarded it in favour of ElasticSearch, a much more elegant and orthogonal piece of software.

Also, I can't programmatically get a list of all "words" in the index with their frequency and the inverse dod freq, etc. With anything lucene based this kind of thing is really easy.