We've been doing continuous deployment at Ars for about 1.5 years. We would generally write tests for our apps before that, but they were somewhat directionless (and awfully easy to blow off for a "minor" change). Once our tests became crucial, we did a much better job of picking relevant tests and feeling their importance.
Many people visibly shudder when we tell them about our deploys. What they don't consider, though, is that manually ensuring a given release is "good" is less reliable than letting a well instructed computer system do it. When you make changes, run your tests, and then eyeball things to make sure everything's cool, you're really just doing unstructured integration testing. You're likely to miss regressions, unintentional bugs in seemingly unrelated systems, etc.