In an empty dir:
git svn clone http://svn.planetozh.com/whatever
If it's from the WP.org SVN repo:
git svn clone --no-minimize-url -s -r31337 http://plugins.svn.wordpress.org/whatever
where 31337
is the most recent revision about your plugin (use svn log http://plugins.svn.wordpress.org/whatever
to get it)
To bring in the full log of revisions (will take hours), use:
git svn clone --prefix=svn/ --stdlayout --no-minimize-url http://plugins.svn.wordpress.org/whatever
git filter-branch --commit-filter 'export GIT_AUTHOR_NAME="ozh" ; export GIT_AUTHOR_EMAIL=ozh@ozh.org; git commit-tree "$@"'