I've had two really productive periods during that time.

One of those periods I spent about 4 hours a day coding, totally focused - get to work at about 5:30 after a leisurely brunch and a 30 minute bus ride during which I planned my coding for the day, jump on a machine and pound the teletype for 4 hours or so, and go home, nearly exhausted. This was writing device driver assembler routines and image processing code.

The second period, I was implementing a prototype of a distributed OS, about 10% of a 3 inch thick spec which defined the whole thing down to the level of small procedures, with a hard 6 month deadline (which was what I had estimated the job would take). I worked steadily for that 6 months on a 40 hour schedule, and finished about two weeks before the demo was given.

I'm currently reading On Lisp and The Four-Gated City (by Doris Lessing), for whatever that's worth.

I'm decent for most of those six hours, and I can churn out maybe 3000 lines a month, but I tend to need a holiday afterwards.

I just quit my cubicle job to switch to iPhone programming, and it's been interesting how hard it is to knuckle down and really get started.

There are times when I have done productive work for 20 hours straight, but most of the time I do about 4-6 hours of work.