If you already have a Canon S90/5 you'll want a Lensmate polarizer. It's mounts in a few minutes and doesn't really fatten up your pocket camera. Once installed, the filter moves on and off the camera with a flick of a finger. The S95 shown below has both the lensmate polarizer (show here extended; it all but disappears when the camera is off) and the essential Richard Franiec grip. I'll say it again: don't leave home without that grip.
You can't apply polarization in Photoshop; only an on-camera filter can make the difference between an annoying, blown opportunity and a great shot.
Midday in NYC: lots of glare. I could hardly look at the side of this building. I reached for the polarizer and the glare vanished.
Minutes later in the Subway I still had the lensmate polarizer on my S95--and got this shot. The car was over-lit with glare coming off every surface.
Polarizers really shine around water. Glare coming off of the ocean can flatten a beautiful scene or simply blow out all the color. But not this time.
Deep within the Pioneer Grove, home of the world's tallest Redwoods you see great contrast between light and dark and very bright areas tend to blow out. The polarizer transformed a flat, uninteresting photo into this three dimensional study.
The county closed this restaurant and arrested the owner after drinking water health codes were repeatedly ignored. Out on bail now and with the restaurant still closed, the owner (not shown here) has become a patriot.