Erm, not being funny but these replies are all totally irrelevant without specifying the type of chain!
I suspect anyone getting 3k miles plus out of a chain is using 8 speed kit or 9 speed and looking after it well. A 10 speed chain is unlikely to last for that kind of time unless it's a fair weather only bike and/or you're a bit of a spinner so don't put too much stress on it. So many variable factors like whether or not you are prone to running rather 'extreme' chainlines etc. (big ring + big sprockets), living near the coast will make a difference too. Hideously dull/boring to debate the various influences... so.
My bike servicing so far this year includes:
Two 8 speed tourers that did 3000 miles fully loaded through europe last year plus another 1000 or so of commuting.... no noticeable wear according to chain checker and hardly any visible wear to cassette sprockets.
My audax bike (again 8 speed) on which the chain/cassette had done ~5000 miles, and since completed PBP too, and still there's just some wear to sprockets and a tiny bit of stretch but again nothing to justify changing either cassette or chain.
Friend's 9 speed road bike, used for two years of commuting and odd weekend riding (estimated mileage about 5000) - chain, cassette and big ring on his compact chainset totally FUBAR'd.
Then there's the guy at the LBS who's just fitted the new XTR 10 speed kit to his MTB and has had to replace the chain after about 500 miles