He had that little stroke earlier this year? Turns out he has early onset Alzheimers.
http://www.boingboing.net/2007/12/12/terry-pratchett-has.html
http://slashdot.org/article.pl?sid=07/12/14/0113224
http://www.boingboing.net/2007/12/12/terry-pratchett-has.html
http://slashdot.org/article.pl?sid=07/12/14/0113224