just found this topic since I have a similiar problem. last 2-3 weeks my macbook core 2 duo bought in 2007 shut down all of a sudden about 3-4 times. Its no problem to start it again.
So, started looking around for answer and finally downloaded temperature monitor aswell as smcFanControl programs to check the temperature.
My MacBooks cpu seems to stay around 77-80 Celsius, even when I am not doing anything heavy. Right now I don´t have any heavy programs running and according to activity monitor no program is taking more than perhaps 10-15% cpu load.
scmFanControl dont seem to have affected anything since the temperature was the same yesterday before I found smc...
I think this is to hot, is it? what is it that causes this? it doesnt feel good that it has just went black like that those 3-4 times and I hope to find what it is before it starts happening more frequently so any advices what to do?