Hrm, does your processor have hyperthreading? On mine, if a process is hammering the processor it'll only spike to 50% as it *thinks* there are 2 processors. So it's actually eating the whole CPU, but only 1 virtual processor, hence the it's always showing %50 and not %100.

If this were happening to me, I'd look for neverending loops that hammer the processor, but, you say it's happening to all the script you run? That's odd, unless you're reusing the code that's causing the problem. :)