During the development of the Quake series John Carmack provided updates through .plan files. These files covered what John was working on at the time and they make pretty interesting reading.
Here are the files to download. Each year of .plan updates is contained in a single downloadable PDF.
In addition, here is a PDF archive of John's comments on Slashdot over the years.
Finally, here is a PDF archive of some of the interviews which John has given.
This content was archived from the team5150.com website which doesn't appear to work anymore.