I got back from 3 weeks in Spain a few days ago; we travelled around a lot, so I managed to shoot a whole load of different things. This was the first time that I'd used a polariser, and was really impressed. The simple explanation of what it does is to cut out the reflections that you see from glass, but it's not until you point your camera at the sky on a cloudy day that you can really see an amazing change. For places like Spain, where there can be bright light and harsh shadows, polarising can stop you from blowing out the sky. I think they're worth the money, photos to prove it coming soon!