A few weeks ago, I decided to photograph Bowman's Tower with my Nikon 18-35mm f/3.5-4.5 lens. It accepts 77mm filters. Since I didn't have a Circular Polarizer filter in 77mm, I decided to use a step up ring and mount my 82mm Sigma slim CP. This was my first time doing so.
What I didn't do was to try it out beforehand. Here's the problem I encountered...I mounted the step up ring and CP. Then I went to remove the hood to flip it in the other direction. I couldn't remove the hood because the 82mm filter was just that much too wide.

Okay,
no problem I thought. So I removed the step up ring with filter attached, flipped the hood then went to mount the step up ring with filter attached. Forget it. There wasn't enough room for me to fit my fingers around the edges of the filter/step up ring to mount them. I wound up having to shoot without the hood (can shield the lens with one hand) rather than to not use the CP.
So I bought a slim profile Circular Polarizer (wide angle lenses have less vignetting when using slim profile filters). Lesson learned!
B+W 77mm Kaesemann XS-Pro Circular Polarizer MRC Nano 66-1066400
Stock photo of my B&W CP filter:
EDIT: By the way, I will not get another Sigma slim profile circular polarizer again (the one I just bought is by B&W, but the one I couldn't use with the step up ring is by Sigma). The first Sigma CP filter developed flaking of the coating so Sigma sent me a replacement (hadn't used either one much and rarely needed to wet clean them). The replacement is doing the same thing. I've used Hoya and B&W circular polarizers for years and never experienced this problem. The replacement Sigma filter was sent in the summer of 2013. I've hardly used it, and it is kept in the plastic filter box when not in use. The reason I went with Sigma is because the filter is 82mm and had a hard time finding a slim profile filter that wasn't over $200. The Sigma was over $100, and since I have owned several Sigma lenses over the years, I expected the coating to last as well as the coating on lenses.