I just replaced my original KMC DX10SC chain at 5000 miles. The Park checker shown in post #4 had just started showing .75% wear. It had been cleaned (wiped down on the bike) and lubed every 300 miles or so.

With 5000 miles of use, my (105) cassette is slightly worn in the middle cogs. Nothing I could see, but the LBS used the Rohloff checker http://www.rohloff.de/en/products/hg_ig_check and it did show some wear. No wear on my chain rings. I replaced my chain with another KMC, plan to maintain it the same way. I imagine that the wear on the cassette will cause the new chain to wear a bit faster than the original did. When the second chain is worn, I expect it will be time to replace the cassette too.