According to the installer the following will occur:
==> This script will install:
/usr/local/bin/brew
/usr/local/Library/…
/usr/local/share/man/man1/brew.1
==> The following directories will be made group writable:
/usr/local/.
/usr/local/bin
/usr/local/sbin
/usr/local/share
/usr/local/share/man
/usr/local/share/man/man1
/usr/local/share/man/man3
/usr/local/share/man/man5
/usr/local/share/man/man8
/usr/local/share/doc
==> The following directories will have their owner set to redacted my login ID:
/usr/local/.
/usr/local/bin
/usr/local/sbin
/usr/local/share
/usr/local/share/man
/usr/local/share/man/man1
/usr/local/share/man/man3
/usr/local/share/man/man5
/usr/local/share/man/man8
/usr/local/share/doc
==> The following directories will have their group set to admin:
/usr/local/.
/usr/local/bin
/usr/local/sbin
/usr/local/share
/usr/local/share/man
/usr/local/share/man/man1
/usr/local/share/man/man3
/usr/local/share/man/man5
/usr/local/share/man/man8
/usr/local/share/doc
This is not acceptable on my system. I hope the client for OS X evolves to not require these changes. Also, I use fink which will cause problems when homebrew is installed.