Insights on what makes me productive

A few insights I've had with regards to what makes me productive:

satisfying "meaty" workplans: I tend to be much more productive if I something on my table I can really sink my teeth into. The best example is an interesting development project with the high-level design sketched up and a road-map with deliverable testable milestones for me to bite through one mouthful at a time.
context switching/batching: switching between various tasks negatively effects my productivity. On the other hand, if I focus on just one clearly defined task for enough time: magic happens.
distractions/procrastination: every once in a while I feel somewhat overwhelmed by a problem to the point of loosing my confidence. In retrospect this usually happens when I bite off more than I can chew, or in other words, attack a problem that is too big at once instead of figuring out how to fracture it into a simpler, more approachable set of sub-problems.
This is routine, and if I just keep at it, the knot in my mind eventually unravels and after a slow start I will pick up momentum and make things happen.
The problem is that I find it very difficult to "keep at it" if any enticing distractions are available. Keeping track of how much time you spend on distractions helps, but I still find that collecting what I need and going offline makes it much easier to get things done. This way if something suddenly comes to mind, I won't go online and check it right than and there (resulting in an expensive context switch) but rather wait until later and batch everything,
quantity of work time: productivity = quality * quantity
Simply no way around it. I pace myself with small qualitative rewards. Reward X for goal Y. But I still commit to working at least 40 net hours a week. Thats 40 hours minimum of pure work. I don't count meals, breaks, private phone calls, etc.
I think thats a sustainable pace that stills allows one to have a healthy work/life balance, and I'm not convinced its a good idea to try and average much higher then that on a long term basis, exceptions notwithstanding.
From my research, the de-facto standard in the rest of the industry is officially a bit higher: 50 hours a week but that includes time (meal/coffee/water breaks, web surfing, workplace socializing) I wouldn't count as "net work hours", so I think my goal is roughly in line.
It is not unknown however for some people in the industry to routinely work 60 and even 80 hours a week, in particular during so called "death marches" to product release, often leading to rapid burnout and disillusionment. Personally I think death marches are a sign of bad management (I.e., insufficient resource allocation and poor planning), and eventually end up being counter-productive in the long run by increasing turnaround, reducing the quality and experience of your manpower and gradually erodes the productivity your existing manpower.

How about you, what makes you productive?