A couple of years ago I mentioned a guide on really smooth user drawn lines inspired by the Paper app.
Here’s a smooth drawing example app and guide submitted by Simon Gladman that uses hermite spline interpolation to draw curves between touch points called SmoothSCribble.
The example provides two views allowing you to see how drawing is using Hermite Spline Interpolation to draw bezier curves, and another with regular drawing.
You can find SmoothScribble on Github here.
You can find the guide over on the FlexMonkey blog.
A nice example showing how to create a drawing app with smoothed out curves.