In theory it's nice to work with, as it forces you to think everything more carefully and consider all error/nullable cases. In practice, integration with XCode is still full of bugs, code completion is crashing all the time, Swift classes show up as missing symbols in Objective-C (but the project compiles fine)... So, it's a bit painful and it slows down the development process.
We will keep it to very small and well-defined pieces of code for now. It's good to learn about it, but it's not productive.