Originally posted by future_retro I believe that Linear Polarizers prevent modern light metering systems from working, that or autofocus
Linear polarizers MAY cause problems with the AF due to cross polarization of light off the beam splitter. This may blind the AF sensor.
All Pentax SLR type cameras with the exception of the LX meter off the focusing screen, so a linear polarizer will not affect metering on all SLRs except the LX.
As polarizing filters and AF don't necessarily go together all that well, and since it will be a fairly rare occasion for the AF to be blinded by cross polarization, a linear polarizer is still a very useful accessory for a Pentax.
I find they work better, and a very good one can be had for about the same price as a relatively cheap circular.