W00t! Right, when I went looking for those photos to demonstrate to you that yes, this is an important expense, I realised how much I use mine. *G*
Once, in fact, I managed to improvise one for a point and shoot digital. While visiting Herself's uncle, himself an artist who does a lot of work with photography though not exclusive, he took me to visit a new building in His Fair City. Mostly clear, somewhat washed out sky with a few clouds. Mind you, he's a staunch film maven. He commented it was too bad my wee digital didn't mount a polariser to bring out the bits of cloud there in the sky.
So I held up the P&S, used the screen (rather than the optical viewfinder) and took off my polariser clip-on sunglasses, held that in front of the lens and twisted it until the sky got nice and dark and the clouds stood out...
Worked, fairly well, and I still employ that trick with P&S occasionally. Does not work quite so well with larger lenses than those, however.