I'm sure he'll be embarrassed that I'm mentioning it, but Nick has just published a very interesting book on productivity techniques.
http://www.nickwinter.net/the-motivation-hacker
I've just finished it and really enjoyed it. There are a number of great pieces of advice on how to be more productive, but I think it'd also be an interesting read for Skritter users as it talks about how the company was formed and gives some insight into the personalities behind the avatars.
James