Wonderful photograph.
To answer your first question; the effects of a polarizing filter are strongest when the sun comes from the side.
However, polarizing filters also remove reflections best when the surface is flat (ie windows, still ponds etc). You may also notice that your polarizing filter can turn (some can) and as you turn you’ll notice the polarizing interprets (strengthens or weakens) the effect of the polarization.
Beyond that, your composition is great. Your framing, the action, the layers and the colors all work together to create a very nice, soft photograph. My main concern is with the photographs balance. As a general rule of thumb, more space should be provided on the side of the frame that an object is looking towards. This applies not only to people but “things” as well. For example notice how direction and composition are tied together in these two images.
http://guyhand.com/picts/about.jpg
and
http://i31.tinypic.com/10rk55c.jpg
I found your image a little to balanced in the placement of your main subject. It’s not necessarily wrong what you’ve done, but you’ll often find that a less formally balance photograph will look slightly more dramatic and catches viewer’s attention a little more.
Other than that; great work! I really enjoyed this photograph.