If you're using OSX and Homebrew and are about to (or already have) upgrade to Mavericks, know that your packages won't work after the upgrade. Here's what you need to do to fix things:
$ xcode-select --install $ brew update $ brew doctor
brew doctor returns any errors, you should fix them.
$ brew upgrade
At this point, everything mostly seems to be working. I did have to manually re-install Maven:
$ brew install mvn
... I'm not sure why.