i am not sjure about 20+ hour spurts unless you include the most valuable time for coding: doing something away from any computer.. coding in you head. I think pg has written about it not too long ago. For me, this coding in your head continues and gets re-forumlated, stored as pseudocode in my head until i can write down the full the implementation in one step. This way i sometimes come to 48h+ of work (including dreaming of code;-) which is just 10percent pysical hacking at a keyboard. /Toni