With regards to heat on Apple laptops, there are three things to remember...
1) Has it room to breathe? I know yours is on a desk, but having it slightly raised at the back is very helpful
2) Room temperature. Hows the temperature in the room you are working? if it's hot, open a window, get a fan on, don't let the laptop sit in it's own stagnant heat
3) surrounding heat? make sure it's not amongst hot lamps or other heat producing equipment.
If your laptop is still heating up a silly amount when it's under strain but is propped up a little, in a cool-ish room and has air to breathe, then just keep a loose eye on the temperature.
Since having my Macbook pro (over 2 years now) I have noticed it's absolute highest temperature is 90 degrees celcius.
Also remember, because you have a temperature control program installed and know it's actual heat, it is easier to be concerned about the heat. what seems silly to you and me in terms of temperature is relatively ok in terms of computer heat.
The majority of Apple users don't know how hot their equipment gets, nor do they want to know, nor do they care, they just use the machines for work, and I know plenty of friends who seem to fry their computers daily but simply because they are using them and don't even know or worry about the temperature.
For me, I ride on the fact that, yes, when i am doing hard core render work, I knock the fans up a little to lower the stress, and hopefully therefor prolong the life of my equipment. A bit like when I drive off from the lights in my car, I don't squeel the tyres so they last longer.
when my laptop shuts down because of the heat, then I will be worried, but until then, I know it'll be fine, and the fact the fans blow hard is only a good thing as it means they are working and doing their job!
Mel