The first time, when I was like 17 years old, I found a program called Eliza (or virtual girlfriend), don’t recall well, a chatting bot. I was a newbie programmer back then, thus this program really impressed me because it was able to understand more than basic questions and it could retain memory and recite what it newly learned.
Today while writing a small introductory article about Expert Systems, I stumbled upon A.L.I.C.E website (http://www.alicebot.org/) which hosts a set of projects aimed at emulating the human brain and how humans communicate and process natural language. To get a feel of this, try to chat with one of the bots:
http://www.pandorabots.com/pandora/talk?botid=f5d922d97e345aa1
Also checkout the image gallery: http://www.alicebot.org/documentation/gallery/ which shows the graph of the bot’s memory and knowledge-base.
I think one day, machines will evolve more and be able to process natural language as easily as human does, it is a matter of time.