My current KMC Silver SL is at apx 3100 miles (half a years worth) and is still in good condition. I strip, clean and re-lube the whole chainset once a month and wipe clean the chain more often.
I usually get to about 18 months on a chain and chain set and then replace the whole lot, but since the last bloody expensive upgrade to Dura-Ace, am not letting that happen and replacing the chain this month.
Stretch is currently minimal... Surprisingly! Then again, as others will vouch, I dont attack hills and tend to spin fairly well..