Briefly, Barney summarises the discussion (very diplomatically ;-) and Lorenzo writes a great first post on the potential and promise of natural language search. Missing from the discussion so far is a broad view of the index side component of NLP search infrastructure - the really interesting part. It is unfortunate that critics are focusing on the behaviour of users (will they or won't they write natural queries) and the ability of the search service to interpret those queries (can they automatically understand and encode the subtle differences?) rather than the more interesting issue of a system that can ingest all the data on the web in a manner that could be called interpretation. Perhaps the only relevant writing on this aspect so far as been the mention of clustering technology such as Vivisimo's which gives the appearance of (a certain class of interpretation - that of word sense) post hoc.
You can see the conversation graph rooted at Barney's original post here.