I don't purport that my experience is anything but anecdotal, but I use the Park chain wear tool and it seems to nicely correlate with what I'd expect insofar as chain wear goes on the SRAM and KMC chains I tend to buy. A new chain shows <0.5% wear, a chain with 2k miles or so may start to pass this guide, but generally shows <0.75% wear and after maybe 3K miles or so, it shows the chain probably needs replacing although I often let it go a bit longer.

I don't think of the Park tool as an absolute but a guideline for monitoring chain wear. For this, I think it works great and is a heck of a lot easier to use than measurement methods.

My chain cleaning/oiling regimen is pretty lax - I leave the factory lube on for the first 500 miles or so, then clean on the bike every few hundred miles with WD-40 followed by a little 90W gear lube, trying to be sure to wipe any excess off. I might remove the chain mid-life for a thorough soak in mineral spirits and dunk in gear lube. About every two or three chain changes, I replace the cassette.

- Mark