How long can my MacBook Pro sustain greater than 100% CPU usage? The Activity Monitor app says my macbook pro 10.7.5 is at 300% CPU usage when I'm trying to install and sync my Bitcoin-Qt client. 

I let in run like this with the fan going crazy for 4 hours without incident, but stressed about it the whole time.

Is that level of CPU usage sustainable? Is this 300% number even accurate to what is going on?

details:


Processor: 2.4 GHz Intel Core i5 
Memory: 4 GB 1333 MHz DDR3 
Graphics: Intel HD Graphics 3000 384 MB
The thing is that 100% CPU usage refers to a single one of the cores in your CPU being fully loaded (or an equivalent load distributed among all the cores). I assume your MacBook Pro has a dual core CPU with HyperThreading; that's 2 physical cores plus 2 logical cores exposed by HyperThreading. Thus, you could in theory achieve as high as 400% CPU usage (4 cores times 100% each).

As to whether it is sustainable, in principle it should be, if the cooling system is in order and the cooling vents are not clogged with dust or blocked by any objects. Even if it's not and you reach supposedly dangerous temperatures, the CPU should throttle itself to prevent any damage.