I have been biking about two years on a bike that I built up, I've ridden probably 6000 miles and have been rotating two chains, they were bought new KMC x9.93. The cassette was bought used off eBay, I don't know how used, but I think not much. I have never checked for chain wear (don't own a checker, but from what I've read a decent steel ruler does the job just as well), and things are running/shifting smooth/quiet enough that I'm not planning on buying new chain(s) any time soon.

PS I lube with Chain-L.