Rather surprisingly, my most productive time is the 2.5 hours commuting on caltrain everyday. No internet access, nobody around from work or home = no distractions. It's been 4 months at this job, so it's unlikely to just be a honeymoon period (knock on wood)

I feel cheated on the days I accidentally get on an express.

This would be impossible if I was still hacking in C/C++ like a year ago. Then, it would take me 2 hours just to get in the zone. Hacking sessions less than 4 hours were simply useless. Now my unit tests make the zone super-easy to find. It's been the biggest epiphany of 2008.