Release Early and Often
Paul Graham called this "one of the hardest lessons for startups to learn" and paraphrased it this way: "The thing I probably repeat most is this recipe for a startup: get a version 1 out fast, then improve it based on users' reactions. Of course, "release early" has a second component, without which it would be bad advice. If you're going to start with something that doesn't do much, you better improve it fast."
"Release early and often."
Who Said It?
Kevin Rose, Google Ventures / Digg