When I'm working on novels, I'm generally sitting at my dining room table, slaving over a hot laptop. ^_^ For general plotting, snippets and fanfics, I could be anywhere. At work, in bed, on the couch in the lounge. I have notebooks for all occasions and a handy stash of Parker pens, so I'm prepared for sudden inspiration. Music is optional, but if I'm listening to it then it has to be right for the scene. For example, if I need to write angst, I'll listen to R.E.M.
Of course, this doesn't help when inspiration strikes while I'm in the bath, which happens quite a lot. I wind up juggling a couple of pages worth of dialogue in my head until I get out, get dried and dressed and grab a notebook. I figure lying back in the water has to be good for letting the imagination fly free, or something like that. Same with going for walks.