Usually my Macbook runs at about 30 - 32 degrees Celsius, but since I have started using a 24" monitor in clamshell mode, I have noticed this rise to about 35 degrees, where previously I had never seen this above 33. I am wondering whether I should be worried and whether this is high, I try to keep it well ventilated and I have the macbook with the vents pointing up, because after all, heat rises.