From what I have read so far (this question in particular), CPL filters are good for darkening skys and improving image contrast by cutting down unwanted reflections. Apart from this, for some different effects, some sites have also talked about cross polarization effects, and the uneven effect on wide angle lenses.
I got my first CPL filter and was playing around with it, and found that it can cut off back light on my laptop screen almost completely. I was wondering if there are any other special effects that can obtained through the use of CPL filters, i.e., anything outside of the expected lines that you have found during their use.