Had the need to convert an SVN repository to Mercurial last night. Here's how the magic went down.

easy_install hgsvn
/usr/local/bin/hgimportsvn http://repository.url/folder
cd folder
hgpullsvn
find . -name ".svn" -exec rm -rf '{}' \;
hg push [repo url]

That was it. Dead easy. Hope that helps someone (or me next time I need it)