I often use arm warmers when I'm out on the road bike, especially useful at this time of year.
They are very good for regulating temperature and you can easily roll them down around your wrists for climbing them pull them up on the descents.
I find they slide down my arms to easily for mountain biking though due to all the bumps and stuff.
I also use leg warmers when it's really cold. Usually in combination with 3/4 bibs for good overlap on my knees.