Slightly off topic, but when I was writing The Geek Atlas one of the things I did was keep metrics about my writing so that I knew where I was, and then I used those metrics to predict the book's delivery date to O'Reilly, and measure how I was doing against the required delivery date.
This was all done in a spreadsheet and it enabled me to see whether I was ahead or behind on my writing. Turned out to be very, very useful.
The Geek Atlas consists of 128 similarly sized 'chapters' (one for each place) so I had a number of key metrics:
1. Number of chapters completed. A very gross progress bar that I could use to get a rough estimate of when I would deliver.
2. Words per chapter. I used this to determine if I was changing the length of the chapter without realizing (which did happen) and correct for that so that the book would be consistent.
3. Hours per chapter. I used this to test my writing speed and work out more accurately when I would be done and also how many hours I could allow per chapter.
This was all done in a spreadsheet and it enabled me to see whether I was ahead or behind on my writing. Turned out to be very, very useful.