An interesting conversation is taking place at Accelerating Future
on predictions by Ray Kurzweil about 2009 that he made writing the book Age of Spiritual Machines
. The book was published in 1998 but he wrote it in the 1996/7 time period. Earlier, Michael Anissmov took Kurzweil to task for wrong predictions. Kurzweil strikes back in a letter defending most of his predictions and says he is working on an essay that will go into more detail about those predictions.
When Kurzweil goes wrong it's usually because he gets the sociology wrong (people don't particularly want speech to text technology that much). My guess is he will be wrong on some of his health/biological predictions made in The Singularity is Near because he underestimates the complexity of the human body. All that being said, he's also been right about quite a few things.