hgsubversion with Homebrew on Snow Leopard
Prerequisites: homebrew
$ brew install pip
$ pip install mercurial
$ pip install hgsubversion
$ cat >> ~/.hgrc
[extensions]
rebase=
svn=/Library/Python/2.6/site-packages/hgsubversion
^D
$ hg clone svn+https://url-of-your-repo [local-name]