I've had mine running 100% 24/7/365 for quite a while with no ill effects. Just see if you can find a good temperature monitoring software for your system, if you can't find one I'm sure people will be more than happy to try to help you find one. My systems stay in the normal operating range easily at 100% CPU throttle. I only have one exception personally which is a desktop at my work which tends to overheat because it is a pile of junk anyway and they turn the a/c off over the weekends. Being summer now, I just turn the throttle down to 60 or 70% on Friday afternoon and crank it back up to 100% on Monday mornings.
If you have a laptop, 100% might make it too warm and cause stability issues. I have a Dell with a C2D 2.0GHz laptop and it barely even gets warm at 100% on both cores. But my Toshiba laptop at home with 3.2GHz P4 gets so hot I don't run it. I guess it just depends on what the specs are.
Edit: Lawrence that's a good point about the dust. Keep a can of compressed air handy, or I personally like a small shop vac set to reverse to blow out all the dust.

Thanks guys,

If overheating is the only thing I have to worry about then I should be fine. I have nice case with lots of vents and fans and my room is air conditioned 24/7 at 67F. My power supply puts out a lot of heat though, 700watt PC-Power and Cooling! However, since I've changed to such a high quality power supply my system has become very stable with almost no hang-ups.