I weigh myself everyday. Once in the morning, after using the bathroom, but that is it. I record my daily weight in a chart, and using that in conjunction with my food log tells me where I could have tripped up to gain a pound here or there. For instance, I now know that I don't do very well at restaurants when there is no nutrition information available. I lose more weight when I up my fat grams. These are things I might not have learned if I only looked at the scale once a week and got a more general picture.
Betty is right (but, when is she not?): when you weigh should be an individual choice. I have read articles that say only to weight once a week, and articles that say weighing once a day is better. Just do what will help you the most.
Kara