Film temperatur effect speed?

How much does the temperature effect the real film speed? I would imagine it would get slower in the winter. Is this noticeable?

I have shot both motion picture film and color/B&W still film well below 0f. -21f on one occasion. The biggest problems in extreme cold seem to be condensation, camera function, and static IME. I never noticed any effect on film speed. I would imagine if there was any effect at all it would be a speed increase, rather than a reduction, but probably not measurable. Teeny tiny things like electrons etc. flying around tends to happen faster in the cold, and film is sort of "powered" by what could loosely be described as an electromagnetic reaction, but as far as an effect on film speed, that's a WAG on my part.

In short, in my experience I have never seen a noticeable variation of film speed when shooting in extreme low temperatures.

I have shot a lot of film in very cold weather. (as low as -35C) As Jason said, static can be a problem. It will show up as little "lightning bolts" on your negative. Stay away from power winders (the batteries usually die anyway) and advance the film slowly to avoid the static discharge on your negs.

I have never experienced any speed or colour shift in any films shot in the extreme cold. It's only the equipment that doesn't like the cold. Come to think of it, my equipment doesn't like the extreme cold either...