I have been using TYPO3 for about one and a half years, at first this was difficult because the documentation is hard to find and when you do find it, it is hard to follow, especially TSREF and the core API. There are some free books at the TYPO3 website, like TypoScript Syntax and In-depth Study or Inside TYPO3, but they still don't answer most questions since they are reference books, and to use them you have to know what your want to reference. I have had to create several extensions for TYPO3 after using it for only a few weeks on-and-off when I had time.