Having ridden over 100k miles, and replaced a few chains over the years, I can definitely say that o-ring chains last longer (at least on ICE-bikes). They do impart a bit of rolling resistance, as evidenced by brammobrian's comments.
A good o-ring chain, IF CLEANED AND LUBED CORRECTLY, and as often as they're supposed to be, will easily last 15-20,000 miles. If they aren't, they can go bad in as few as 5,000 miles. Remember, ALWAYS replace the chain and sprockets as a set. If you don't, you'll see significant reduction in chain life, as the worn teeth on your sprockets rapidly wear out the new chain.
thus ends my soapbox moment...