do you weight your self every day ?

Twice a day. I log the lowest amount of the two in my SS.

The data is invaluble, from trends and calorie data, you can extract what your actual surplus/deficit is and what intake you would maintain at.

I only do if I'm really pushing myself during exercise. It's a good way to keep track of fluid loss so you can re-hydrate properly.

Yes, unfortunately, I too, am one of those "chained to the number on the scale" people. I weight 3-4 times a day (not kidding). I weigh before I workout in the morning, after I workout in the morning, before I workout in the evening, after I workout in the evening. Of course, I am also in a competition (imagine Biggest Loser but on a gym-wide scale), so that might have something to do with my obnoxious tendencies (or not, LOL).

I weigh myself every morning, without clothes, immediately after going to the bathroom but before drinking or eating anything. I figure that's the best way to get a consistent value.

Even with doing that I still notice swings of +/- 2 lbs. Google "The Hacker's Diet" if you've never heard of it. He uses exponential smoothing to filter out the noise of the day to day swings to give you a moving average that's pretty damned reflective (in my experience) of your day to day success or failure at healthy living. The formula is simplistic enough to create on your own in Excel without following his whole program, or you can use his free online tools.

I use MFP as my food diary, The Hacker's Diet as my weight diary, and various fitness apps (SportsTrackLive is an excellent one for runners and hikers) to track exercise. MFP gets the data entry for weight and exercise too, but in this instance I'm more concerned with the daily moving average from Hacker's Diet than the raw numbers.

I weigh myself naked every morning and log that, and I weigh myself at the gym before and after my workout to see how much water I lost and make a note to drink lots.

The number flucctuates which is fine, mostly I feel really happy seeing my weight because I'm so close to my goal! It keeps me really motivated, to see a reminder that hard work pays off

The flucctuations are crazy though, I can be 119 in the morning and 123 the following morning, even though everything was as usual.

I would think if you are really far from your goal, you should weigh in less because of how much time needs to go by with good behaviour before you see what you like. It will feel like groundhog day which can be discouraging... When I was 131 I definitely did not want to see those numbers!!