Nice one. Three days seems way too excessive though given the specs of your box. I'm assuming you've used radiosity in there for the image. You might want to look at reducing the rays per evaluation somewhat to see if that will produce an acceptable render in a shorter time.
Also, there is the shadow to the left of the desk as Bullet_evader has already pointed out. Other points are: 1. The monitor on the left still looks out of place. It actually looks as though its absorbing light rather like a black hole
The one on the right looks fine. 2. I'd take another look at the desk texture. Either shrink the scale of the texture, or even add some blurring/texture aa to it to prevent the obvious atifacts that are showing.