Sweet sugary goodness... this app rocks. I'd been having trouble in PreCalc understanding all the relations between radians, degrees, sines, and all that nasty stuff. Being a visual hands-on learner, this has helped tremendously in understanding trig.
Other features I'd love to see in the future would the ability to show and calculate tangents/cotangents, secants/cosecants, and copy and export functions to place graphs into other docs.
The app did spaz out and lock (i.e., spinning beachball) the first couple times I opened it. It seems to be fine now, though. Bizarre, whatever it was, but it works now. :)