It depends a lot on the CPU; for example, my Athlon64 X2 has a maximum design temperature of 65C while the Core2 Duo in my laptop is designed for 105C. Most chips these days have built-in thermal protection that will scale down operations if you exceed design temperature to prevent sudden death. There are many factors that determine whether said temperature is "ok", but if you're running close to or at the design temp CPU life is probably going to be shortened significantly.
If you have an Intel processor, thermal spec is easy to find:
http://processorfinder.intel.com/Note that laptops can be pretty tricky; just because the CPU is ok doesn't mean the heat will play nice with other components. I had a Pentium 4 laptop a while ago that pretty much melted down... All was fine when you started it up cool, but as it warmed up things like USB ports close to the CPU would stop working. The cooling system was sufficient for the CPU itself, but it didn't efficiently evacuate the heat from the laptop--it let too much spread around to other components.
