I had the same issue... macbook pro 2006 2.33Ghz. After SL installation it started run progressively hotter and hotter over the months. It actually started about one year ago when i still had 10.5 on. I tried all the software solutions (PRAM, etc), and also shoot compressed air in the vents, with no results.
Then i read an article about dust collection in the vents and replacement of thermal paste. As someone else on this thread, I followed the iFixit instructions to take it apart (you need to be very careful but it's not rocket science and i am not an technical guy). Here's the link to the instructions i followed:
http://tinyurl.com/349l4pu
Once i took the laptop apart, i cleaned up the vents that were literally clogged by dust. Cleaned up the old thermal paste from the CPU's, GPU and heatsink that was pretty much dry and spotty, and applied a nice coat of Arctic 5 thermal paste. Reassembled the laptop, said a couple of prayers, powered it up and it worked flawlessly, and i am now running at least 10-15 celsius degrees cooler. Before i was running around 70-75 celsius degrees in light to medium use conditions (mail, entourage, a couple of safari windows) and now i rarely go over 55. I then opened a few youtube videos in separate windows (which used to be a killer for my mac, often times forcing my mac to quit), excel, powerpoint, and whatever else was already open. Usually it was running between 85 and 89 with peaks well over 90, and after the "surgery" it was pretty much around 70 degrees, with peaks of 76.
I can say - so far - that i have my old Mac back. I was quite annoyed and ready to trash it to get a new machine when it kept acting up and running unbearably hot, but i think i will give the old guy another chance... all in all it's still the most reliable laptop i've ever had.
Please note that my machine was purchased in 2006 and the Apple care coverage was long gone, so i did not have any warranty drawbacks. If you have a newer machine that it's still covered, opening it up will invalidate your warranty, so be careful if you go down this path.