I think in addition to all of these, the stakes are pretty high - when you're dealing with such an incredible number of users, you tend to weigh your decisions much more carefully, and learn to spend a lot of times poking holes in your thinking. It's one thing for a small startup site to go down for a few hours, it's another when Gmail or Facebook have to deal with a crisis - millions of people are affected. This imposes a lot of humility and discipline in your craft.

I always love seeing your process, though I second the comment about Slicy, which does a bunch of the 1x/2x work automatically. I would love to find a shortcut way to scale layer effects from 1px to 2px and vice versa. That's usually the most annoying of the scaling changes.

I'm curious - why do you prefer groups to layer comps? I find the actions for quickly exporting layer comps to files for previewing flows extremely helpful.

Single PSD with Layer Comps all the way! Easiest way to track things. When the file becomes too large, just Smart Object certain states.

This bit is crucial: "Missing credits - One of the confusing things that I found tedious was the lack of credit in pieces and projects as to who did what. It is not only hard to evaluate your contribution but also what you are capable of doing. It is also very unlikely that you did the whole project by yourself and if so, say so."

I have just switched to an adjustable height desk and am trying to work standing up as much as possible (targeting 80/20 standing/sitting). It's been fantastic, I feel more active throughout the day and I seem to attack work problems with a bit more focus. I also design using a Cintiq Wacom tablet which is angled, so I think that helps tremendously as well.