I have been using the polarizer a lot during the summer with my photos.  The high sun provides harsh lighting and a lot of contrast and I have been using the filter to cut down the light and to try and reduce glare from white aircraft fuselages.  It has mainly been used on my longer lens also helping to get shutter speed down to provide some motion blur in backgrounds.  However, I did put it on a wider lens when some planes were taxiing past me.

This proved to be a mistake.  It did take out some of the glare and make things a little more balanced from a contrast perspective but, when used on a wide angle lens, it did result in some unintended effects in the skies.  The polarizer effect is quite varied depending on your angle relative to the sun and this results in quite a dark sky in one part of the shot and a brighter sky in the other.  The result is an odd effect which distracts from the plane itself.  Consequently, I have avoided using this filter for these shots more recently.