I have been working 25 hour weeks for a little over a year now, but agonizing over finding a good number for years before that. I've found that for difficult problems to crack, I may only work 1 or 2 hours per day. But for easier stuff like initial setup, a little refactoring, translating wireframes to layouts, etc, I can easily manage 6 or 7 hours per day. 8+ is too much, and working 3 or more days in a row at that…
Hehe, the web of interests sounds very familiar. I'm using pocket (getpocket.com) to cut down on the number of tabs though, maybe it would be useful for you as well.
I currently use Instapaper for longer articles and stuff I 'must' read, Pocket for more whimsical stuff or resources and things I can safely never read, and OneTab as a 'temporary storage' for everything that doesn't quite fit these other two categories.