Cal Newport of at Study Hacks [1] has been talking about this type of stuff for a while. He approaches what he might call "a philosophy of deeply thinking about hard problems" from an academic standpoint, but I think you can apply it generally. He's done some pretty good interviews/detailed posts on the topic.

I really think that pseudo-work is a killer. PG talks about this a bit here [2]. This type of constant context switching is dreadful for productivity, and also stresses you out. Saying that, some startups actually do require 100 hour weeks. Read Max Levchin's interview with Jessica Livingston [3]; he spent like 4 days getting the Paypal demo ready, and then fell asleep at the restaurant table after showing it to the VC's. But there are also times when you have explore; Max said he had this later when Elon Musk came in as CEO and was trying to change direction. Max had tons of free time, so he started playing around. This led to the discovery of the fraud detection system that probably saved the company.

So there's a time and a place for 100hr weeks, but you can lose sight of the big picture if your head's to the grindstone all the time.

[1]http://calnewport.com/blog/

[2]http://www.paulgraham.com/selfindulgence.html

[3]http://www.foundersatwork.com/