We've been using Edgewall's Trac and a plethora of Trac-Hacks to manage a large development project. It serves as a front-end to our SVN repository, it is our project wiki, and we've progressively built a nice toolchain to tie it all together. (We especially love the integration between Trac and SVN using Tortoise, TracExplorer, and post-commit hooks.)
But, like any tool, there are a variety of ways to use it, often beyond the scope of the original design. How are you using it? Has anyone had experience/success opening it up as a customer support tool?