Interesting looking chatbot called Arckon from Don Patrick which seems to take a development line far closer to what I'm after than most I've seen. He reports using a grammatical parser to understand the input, then rather than focus on Parts of Speech he extracts the implied triples in the sentence, and then uses a triples base and inferencing to derive the response, apparently he "formulates his own sentences dynamically by feeding the relevant facts through a complex grammatical template. The only pre-programmed answers are a few dozen standard manners, like "Thank you" and "You're welcome"."
The following diagram shows how the triples extraction works:
And an example exchange:
Lots more on his website and blog at: http://artistdetective.com/arckon/