Never had a problem with it - like any other overclocking there are risks, but it shouldn't do anything silly. It will push your voltage up to 1.55v which is about as high as you'd ever want to take a PII - but you may not want to run it 24/7. There's a thread by me a page down or so asking about the voltage.
I'd also note that it tends to do the automatic clocking using the HTT link - you'll probably get better results using just the multiplier at first.
Finally, turn cool'n'quiet off while you're trying to find your max overclock - it just makes life easier working out what clocks you're aiming at and seems to make overdrive a little faster.