Oops. Forget to reply to all.
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From: Colin Adams
It depends on what you use the code for. If I run an overnight report for the trading book of my bank in 16 hours, it is not acceptable and is a disaster. If I run it in 8h, it's OK-ish. In business settings, you often have strict deadlines and optimizing the code to be 2x faster can make a huge difference, as you change from missing the deadline to meeting a deadline.
Seconded. I remember once being asked to examine a certain batch program for performance improvements. I spotted an obvious inefficiency, and made a recommendation, which was implemented. It saved something like 10 - 30 minutes on the overnight run (which took hours), so I was disappointed with the result. But the client was delighted, as the run now fitted into the batch window.