Season 1 did good. It had NCIS: LA as the lead in. Then when it started doing worse, they stuck it on Sunday versus Desperate Housewives' last season which hurt, but it still got renewed, and it's basically been rated this season the same as the last. It performs on par or better than The Mentalist, but what it has going in it's favor is that it hasn't reached syndication while Mentalist has. Hopefully CBS keeps it around for another year so they can sell it.
Edit:
Everyone seethe at my iPhone wallpaper. Lightning shits, and anyone who disagrees shall be transformed into a Cie'th and promptly slain.