I gave a talk at Scotland on Rails last year about image processing in ruby, including using OpenCV. Getting it working well with Ruby is a bit of a pain, but it can be done. My fork of the ruby-opencv gem is at http://github.com/bantic/ruby-opencv and examples of using it to do face detection are at http://github.com/bantic/image_labs

Nice article. Still a little bit tough to follow though. I actually just finished getting OpenCV face detection working with Core Video in OS X, it's accuracy is very impressive.