I was assigned to a project where all the testing on the project was being done manually. Since I had experience with automation, I suggested I could help them by automating some of the regression tests.
I talked with the rest of the QA team who did the manual testing and we decided what should be automated. Since the client had not yet given approval, I prepared a short demo of the most basic tests cases to show them how much it improved our work. They loved it and asked to have most of their testing automated.
I decided to use Selenium and implemented all my tests in Java and JUnit. After the first regression tests finished, we set up continuous integration with Hudson so that the test suite would run every night and give us reports of any present issues. Eventually, I expanded the testing to other projects for the same client, even for some with Flex, for which I used Selenium-Flex along with Selenium and JUnit.