Start a tweet with @letpgfinish, and it will be finished as if by Paul Graham himself.
This was a weekend project I undertook with a couple of friends just for fun. The original one was @letkanyefinish, so you might like to try that out too... in fact, it seems to work much better (funnily enough, there's a definite inverse relationship between literacy of bot and literacy of its human counterpart).
Anyway, the output is based on pg's essays and various tweets/quotes. Having used HN silently for a while, we thought we'd share this - so hope you enjoy :)