Absolutely, tom - reference sytems are a must. The point of (good) mixing being to have the sound translate well to any other environment, and still sound within the (subjective) tolerances of how it 'should'. You cant possibly have too many other systems to do that with (other speakers, headphones, stereos in other rooms, your car, mp3 player, mates setups, anything you can get your hands on). Accurate headphones you know the sound of should be on hand at all times, regardless of how meticulously you'd set up your listening position, IMO (if nothing else, for accurate panning)
On the residential environment - I dont think so, so much. You'd think my lounge would have a linear sound, because there are couches on two walls and a big bookshelf on another; not so, its one of the least linear places I've heard. Symmetry is a huge problem for standing waves, though - the less even your rooms shape the better, as a rule (mine aint so good - its quite symmetrical with a really strong mode at 130 and an 80hz is almost eliminated in it, all things being equal - it was hard work getting it to be (nearly) linear!).
But yeah, as a rule sticking a couch opposite your speakers cant hurt, and will probably help, and the more corners are filled in with sound-deadening things (of any sort you can get) the better.