I have a macbook pro late 2007 2.2 core 2 duo. Just installes SL a few days ago. My fan starts kicking in at 20% cpu load.... and it's hotter than usual. Before I could use a text editor (celtx) with the computer on my lap, but now I can't, it becomes too hot. Hell, the fan starts kicking in watching a video on youtube... More people are having this issue. If you have please post in this thread so Apple notices it http://discussions.apple.com/thread.jspa?messageID=10068996 People are recommending reseting the PRAM and the SMC. Haven't tried that. Just noticed the 10.6.1 update... will try it to see if it helps.