Animating a shape with CoreAnimation

If you are writing this for iPhone OS 3.x (or Snow Leopard), the new CAShapeLayer class should let you do this kind of animation pretty easily. If you have a path that maintains the same number of control points (like in your case), you can set that path to the CAShapeLayer, then animate the path property from that starting value to your final path. Core Animation will perform the appropriate interpolation of the control points in the path to animate it between those two states (more, if you use a CAKeyframeAnimation).

Note that this is a layer, so you will need to add it as a sublayer of your UIView. Also, I don't believe that the path property implicitly animates, so you may need to manually create a CABasicAnimation to animate the change in shape from path 1 to path 2.

EDIT (11/21/2009): Joe Ricioppo has a nice writeup about CAShapeLayer here, including some videos that show off these kinds of animations.