Circular polarizer

Does anybody know if you have to increase any f-stops when using a circular polarizer?

Maybe.

The meter should compensate for the filter, but sometimes it doesn't always manage to hit right on. Usually it's only 1/3 or so extra, but I have gone up to +1 at times.

Polarizers may throw off your meter because they're cutting out a lot of the glare, which is likely to be in secondary areas of the picture but still affecting the meter. Net result, your primary subject area may be underexposed. When in doubt, open up and check your histogram.