First off, I had the error on line #106 too, and it did get fixed by saving pretty permalinks.
I also have the issue of the plugin not working on themes whose human-readable name (not the directory name) have more than one word, but since this is easy to change in a theme, it's not really an issue.
However, once I do switch themes, if the other theme doesn't have a widgetized sidebar where the dropdown list is shown, it's impossible to come back to the original theme without clearing cookies off your browser.
Not to play this plugin down at all, but I found "Theme Demo Bar" in the WP plugin repository - it gives an almost pretty link to try one of the non-active themes, and doesn't set any cookies. The "bar" on top for switching themes is optional, so if it's getting in your way you don't enable it at all. Just saying :slight_smile: