What is Reddit's opinion of Cornerstone?
From 3.5 billion Reddit comments

➔ Cornerstone website

By popularity on Reddit, this Service is:

#53 in VCS apps

1 review of this app found across Reddit:

Not your question but the tools I use for SVN are:

Cornerstone http://www.zennaware.com/cornerstone/index.php for SVN client

Beanstalk http://beanstalkapp.com/ for SVN server and deploying code to my servers.