The previous owners of our house had painted the living room this lovely shade of puke, and got the mirror in there. While some people feel that a large mirror makes the room look bigger, I have the opposite opinion. For a large space like this, it just reflects the clutter, especially since you can see the kitchen area.
We also decided to paint the living room before we moved in. That was a bad first project to do. With no idea about how to paint anything, we decided to tackle the biggest (1000 sq. ft of wall), darkest and most strangely shaped room in the house. It took us four coats (2 primer & 2 paint), one week and one nervous breakdown to cover up the green.
I did like the way it turned out, and think it opened up the place a lot more than with the mirror.