As far as within the theater world, yeah she is pretty famous. I wouldn't put her up there with Bernadette and Patti, but she certainly is very well known.
As far as mainstream TV and film fame goes, she's not really that famous. If you were to poll 10 people on the street (not in NYC) I bet less than half would know who she was. People may know her as the woman from Pushing Daisies but she's hardly an A or B lister. And like someone already said, her recent gig hosting the Critic's Choice Awards probably didn't help her that much. And I doubt she gained much exposure from only being in half an episode of American Idol.
Incidentally my parents, who are causal theater lovers have no idea who Kristen Chenoweth, and Patti LuPone are. But they are familiar with Michael Crawford, Bernadette Peters, and Audra McDonald.
"You drank a charm to kill John Proctor's wife! You drank a charm to kill Goody Proctor!" - Betty Parris to Abigail Williams in Arthur Miller's The Crucible