This looks like a great plugin. Thanks for sharing it!
Unfortunately, I've got a scenario that prevents me from using it. We suppress the admin bar on our site, so there is no "Switch back" link.
We use the plugin, "Remove BuddyPress Admin Bar" to suppress the admin bar. FWIW, we also use s2member, which I see mentioned in http://wordpress.org/support/topic/plugin-user-switching-no-switch-back-option?replies=2 .
For now, I'm using another plugin to get user switching ("Browse As"), as it does not depend on the admin bar. It appears User Switching is a more robust solution, so I would happily switch to it if there was a workaround. I recognize I'm probably in a pretty unusual situation, so this is not a feature request.
Thanks again for contributing your work to the community, John!