In 1966 Joseph Weizenbaum wrote Eliza, a program which simulates Rogerian psychoanalysis by capturing text strings from subjects responses and posing questions back to the user. While not exactly "AI", Some users had difficulty in telling interaction with Eliza from interaction with a human being.
Move to August 2000, Kevin Fox of fury.com, using a freely availible Perl version of Eliza, a spare Mac, some AppleScript, the AOL Istant Messenger and some accounts which have a high frequencey of random hits unleashes "AOLiza" on the internet populous.
His results are posted on http://www.fury.com/aoliza/index2.php
Of the thirty one (as of 8/31) "conversations" with AOLiza (since 8/15/00), only two individuals displayed any knowledge that they were speaking to a program. On the other side, two individuals revealed rather personal information to AOLiza.
I am almost positive that this type of thing has been done with IRC bots in the past, but rarely have the results been posted in such a well thought out way. They are at the same time funny and sad.