My ray tracer can now load .ply models and uses kd-trees (TA-B traversal) for acceleration. I used the high res model of the Standford Bunny which has around 69,000 triangles. Without any form of acceleration, the render times are over 1 hour for the basic ray tracer.
With kd-tree acceleration, it requires about 14 seconds to build the tree and the render time is cut to approximately 24.5 seconds. The machine used was a 2.26 GHz Intel Core 2 Duo MacBook Pro with 2GB of RAM. Below are the results at a smaller size preview. Click on the image if you would like to see the full render size.