By default, it will append a "g" to all the coreutils at least, like ls -> gls, sed -> gsed, etc. And things that are already default on OS X, like curl, perl etc, will not be symlinked into /usr/local unless you force it.

But personally, I changed my coreutils over a year ago to the GNU ones (via symlinks), and I force link every single package, I've never had a single issue.

Though our use cases may be different, and you may have issues. In which case you can just `brew unlink $package`.