Before jumping on iPhone development with OpenCV make sure you master OpenCV on a standard platform, like Windows/Linux/Mac OS X.
Also, decide which interface of OpenCV you prefer to use: C or C++
There are the results I got from using the search box on stackoverflow:
Detecting a circle of a specific color (or gray level) with openCV
Detect Corners of Triangle in Image on iPhone
OpenCV Object Detection - Center Point
How to recognize rectangles in this image?
and these are results from Google:
Tracking colored objects in OpenCV
Circle recognition using openCV
Fast OpenCV Circle Tracking (check the description of the video for tips)
This series for OpenCV is great, specially this one: Vision for Robots 5 of n: Hough Transform
OpenCV Eye Detection
Face Detection using OpenCV
