I can physically be at work on a friday afternoon, but I guarantee I'll accomplish nothing other than being interrupted. It got to the point that I wouldn't even try to do stuff on Fridays... I'd just plan to sit there, maybe surf the net all day, until I get interrupted (which usually didn't take long). Its too risky to try to do stuff knowing you're heavily impaired by interruption, so trying to do nothing at all on Friday actually measurably improved my overall long term productivity, which I thought was interesting.
That really depends. I have been working from home for 5 years now. And the fact that I'm in a room with no view from the window and no human interaction drives me crazy, so the solution that works for me is to usually go to a coffee shop and work from there. I actually found that I need all the noise and crowd in order to focus, I can get a lot more done in that 1 hour at the coffee shop than the whole day working at home.