yes, joules is the size of the energy spike it can absorb. Its basically watts per second so if you have a 100w spike thats 10ms long it would be 10000 joules. its a good thing spikes arent usually that big and certainly not that long. <grin>
And by wearing out I meant the strip itself. The circuitry used in most of them wears out a little with every spike they absorb so every year or two, replace them.