circular polarizing filters are needed only for cameras with polarizing elements in the light path or in the light metering system. These are all autofocus cameras, Leica SLR's and some other brands. But there is no problem with "normal oldfashioned" cameras. In most cases circ. pol. filters are more expensive than linear ones.
Yes, I am fully aware of that. I, though, will be using the circ. pol. filter on Auto Focus hardware as well (both Film and digital).