Most computer desks are probably the worst for computers due to the fact that they are rather enclosed. Not only do many larger mid-towers not fit, but with the rear on many, it doesn't allow for good airflow. On both my of desks, I have removed the back so my computer can semi-breath. Still, I feel it would do better just sitting in the middle of the room
Well, I've heard that the computer shouldn't be near a radiator or a window. Mine is about 10cm from the radiator and just under a big window. Worst place to have it.