I agree with wahoonc that modern narrow (9/10/11) chains don't last. On my 9-speed rigs I was only getting around 3000 touring miles. I'm sure the fact that my touring includes a good bit of back-country dirt and gravel is a factor. It's one of the reasons that I built my latest touring bike with the beefier chain on an 8-speed drive-train. So far the 8-speed chain measures fine after 3000 miles.

For those doing a cross-country tour on 9/10/11 speed chains I'd definitely start with a fresh chain and measure or have it checked at 3000 miles. Those of you who wait for shift-skips are making a mistake, in that your chain-rings and cassette are probably compromised by that point.