Once again, Michael Lopp says it better than I ever could:
Context isn’t just the art of knowing where you are, but the illusory and friction-free belief that you know where everything is.
Questions like: “Where is that?”, “How do I find it?”, “Don’t I already know that?” are mental speed bumps that are context- and Zone-destroying distractions. Why do you get pissed off when the phone rings when you’re in the Zone? Because you know you will shortly forget where you are. This is why when I’m working on a project of size, I’m most confident and most productive when the complete set of what I currently know is sitting directly in front of me.
It's been a few weeks and I still can't express how much more focused and productive I feel on Lion, with full-screen apps and Mission Control to tie everything together. For the first time, I feel like I spend more time working than organizing my toolbox.