Another Google Plus to Atom/RSS service has turned up.
http://pluss.aiiane.com/

Discovered on the Google Issue tracker request
http://code.google.com/p/google-plus-platform/issues/detail?id=139

To go with my own PHP attempt.
A single file PHP script which serves public posts to a Google Plus account as an Atom feed. https://gist.github.com/3938374

Why, oh, why has Google still not provided this ?