An updated homebrew-iojs formula is maintained by @aredridel and is available with just one command.
As of iojs 2.0.2, Homebrew ships with its own formula for iojs. This isn't preferrable, in my opinion, since global npm packages aren't being ran properly.
If you'd like to use this anyway, simply doing brew install iojs
is not enough. To get iojs working on Homebrew You will need to unlink node
first then use link --force
to install iojs.