I don't think it's healthy to obsess about one's weight. There's enough fluctuation day-to-day, especially with consumer-grade bathroom scales, that checking every day can be the cause for more trouble than it's worth.
That said, I weigh myself every day. I know it's inaccurate. The key is that I don't obsess over single pounds, nor do I think that a gain or a loss of a pound is due to something I did the day before. I do weigh myself at the same time every day; in the morning, after a shower. Hopefully that helps to minimize the amount of daily fluctuation that's due to stuff other than the reasons I want my weight to change.
There are four main factors influencing what the scale tells me:
1) Body fat. I want to burn this off.
2) Lean mass. I want to add this.
3) Water weight. Drops the most the first few weeks doing low-carb.
4) Digestive mass.
5) Temperature and maybe humidity.
Digestive mass decreases on days that I'm fasting, since I continue to evacuate, without replacing it with any new digestive mass. On days that I break fast, I add mass; so one can see a sizeable jump up in weight after coming off a 36-hour fast. On normal, non-fasting days, this bit is probably fairly consistent, tho I know large meals will skew my weight.
The goal of weight loss is really item #1 up there -- burning body fat. I don't want to lose lean mass. I'm continuing to walk (about twice a week at this point, 6 miles total) and do intensive strength training (I'm shooting for every four days but hitting every 5-6), which will build lean mass. The other major component would be making sure my body isn't catabolizing lean mass, by making sure I've got energy stores available. That means staying away from the carbs, giving my circulatory system a chance to pull fat out of adipose tissue.
So why weigh myself every day? I do it to enforce good habits. If I lose a pound, I know it's not because I ate good yesterday; it could be because of fasting, or water weight, or temperature fluctuations. Howevery, I tell myself that it's because I ate good. I tell myself that it's because of good habits. My point isn't to lie to myself about my weight, but to help reinforce those good habits. I want a positive association with staying on-diet, avoiding carbs, exercising, etc.
I think there's a definite line between believing something that you know isn't true, and building an emotional connection. I've given my brain enough evidence to believe that I shouldn't be touching wheat, but my heart (um... my emotional center) remembers that I love pasta. What I need to do is change my heart. In this way, I'm using my brain to drive my emotions to where I want them, rather than letting emotions win over my eating habits.