An informative article on chain "stretch" (roller wear) and measurements...  
 
http://www.fagan.co.za/Bikes/Csuck/STRETCH-MEASURE.htm  
 
I just had my chain (2-1/2 chains, actually!) replaced, thanks in part to a friend being a busybody   on Sunday and going around and measuring everybody's chain with his gauge... I was a bit surprised, since there's so much chain on the bike, but this one has gone about 6,000 miles... I was apparently well past time, and had been hearing some noises from the cassette in high gears, so I took it in. The LBS doesn't think the cassette needs to be replaced, fortunately, but they definitely agreed with the stretch gauge...   I'll see how it acts over the next couple of days, before Sunday's 200K!
 
And here's the main article about "chain suck"
 
http://www.fagan.co.za/Bikes/Csuck/
 

After destroying a cassette with a worn out chain (and 2 chainrings to boot) I bought a Park CC-3 and use it every time I clean the chain. still well within the .75% limit.
 
Opus

Nelson,
 
My Corsa chain has 5200 miles on it. That's why I kind of expected it to be in the .75% wear range, if not already in the 1% replacement range. But, I do tend to be a spinner rather than masher, and I've used Dumonde Tech since a couple of months after I bought it, so who knows? It may last a while yet.

Glad I could help with some timely info...