Explaining caps - voltage

[überfuzz]

Every now and then I see folk writing that electrolytic capacitors should be working fairly hard to stay alive. The voltage rating on the cap should be well over the estimated voltage, but not ridiculously high. Is this true for other caps types as well?

I use a lot of Polypropylene and Polyester capacitors. Is it safe to have them running on 'low' voltages. In other words, will it shorten the lifespan?

[Merlinb]

In other words, will it shorten the lifespan?

No, the voltage thing only applies to electrolytics, and even then its not a big deal.

Electrolytics tend to get used to the voltage they normally operate at. If you run a 400V electro at 10V for a long time (months), and then suddenly apply 400V, there is a chance it will draw a lot of current like its being run 'over voltage', and may be damaged. I can't remember if there is some other reason to operate an electrolytic close to its ratings..?