There are a number of established and professional level open source Content Management Systems (CMS) available, so what prompted your decision to use TYPO3?
Some of the main advantages we found with TYPO3 include the flexibility provided by adopting a CMF configured to operate as a CMS. By that I mean that TYPO3 is effectively just set of core Enterprise class services, such as granular security, with additional functionality provided by the 900 or so available plugins (called extensions in TYPO3 speak). We were also impressed with the large amounts of quality documentation available in multiple formats (OpenOffice, pdf, video) and languages.