You should really add some filters to this plugin. Because of the way your plugin handles changing the title (which uses output buffering and filters the stream, not a good idea) doesn't allow me to add anything to it. If you're going to make the plugin override anything I "hardcode" into the TITLE tag, you should provide some filters in the plugin so it can be manipulated there. This is where AIOSEO has a one up one you. Michael has used filters in all practical places. I suggest you do the same!