Volenti - the WV you sometimes see on caps stands for Working Voltage. (I hate caps rated that way as it takes into account derating, and they usually don't spec what derating numbers they used or what circuit configuration. Just give me the true rating)

An additional failure mechanism you have in caps associated with AC voltages is the amount of ripple current versus the ESR value of the cap. If the ripple current is too high, the cap heats up and can indeed go terminal ;)

hmm, I have some here rated at 350V, that are blown