To me this boils down to two basic points.
First, you have to understand what the scale can and cannot do: What it does and does not measure, why weighing under inconsistent conditions (i.e., more than once a day) is pointless, etc. (It amazes me how many people fail to understand that ...). You might take a look at this article for a good explanation:
http://www.primusweb.com/fitnesspart...ight/scale.htm
Once you have a grasp on the science, then you have to evaluate how those numbers make you feel. If you understand the science but those fluctuating, inaccurate numbers still affect you in a negative way emotionally, then stay off of it. If you can take them in stride and maintain an objective view, or if they keep you honest, then weigh as often as you like. You have to do the things that HELP you, not drag you down, and sometimes that goes against the conventional wisdom of what "dieting" is all about.
I stayed off the scale for six months, essentially, because I needed to concentrate on changing my lifestyle without the distraction of worrying about how much weight I lost from day to day or week to week. Since then I've gone through periods of weighing every week, of weighing every day for a couple of months to understand my body's patterns, to weighing once every couple of weeks or less.
I've said before that if you are "dieting" and "losing weight," you live and die by the scale, and you will always maintain a dieter's mentality of being good/bad, on-a-diet/off-the-diet, etc. If, however, you are more concerned with doing that lifestyle makeover, then the actual weight loss becomes a side effect. Sure, it's a huge boost to see those numbers go down, I confess I'm just as happy as the next person when I go through a vigorous loss period or pass a milestone. But, I finally understood that just as the weight was a SYMPTOM of a life that was out of balance and unhealthy, losing the weight is a by-product of a life that is healthy and balanced. The point is the life, not the weight.