Well the maximum temperature before your CPU is in immediate threat of being deep fried is 90c for most of the Intel Atom chips that are present in Netbooks.. I would no where recommend testing that limit on your cpu.
It is important for your system's health to keep it cool. Cooling also helps with longer battery life I suppose.
I always tend to keep my eee pc under 45c but on some occassions it heats upto 56c where I start closing the used applications taking up CPU cycles.
Also, I use applications like HDD Health and Speed Fan to monitor the temperature as it seems to work with most of the CPUs.
