I'm assuming these Macbooks that ppl think are too hot are the first Core Duo or C2D laptops they have used for any period of time.These are screaming chips,I would be more worried if they didn't get hot.
My macbook pro began running hot... 70 then 80 and then 90. I ran the applecare diagnostic 'TechTool Plus' and it is now running back at 65-75. I'm not sure what it did but it worked.