Depends on the program. Any program that only or mostly calculates something will use 100% CPU. Only programs that wait for user interaction or use network, disk or some other external device heavily (and thus often wait for the network or the disk) will use less than that.

If you execute a perl program like

$a=<>;
[download]

and it still uses 100% while waiting for you to input something, then it is time to worry ;-)