I'm terrible for weighing every day. Personally I think it has its uses, like Morrigan said I've learned alot about my body, which foods make me retain weight etc, and I sometimes find it useful when I'm finding it hard to get my head in the game (lots of "Oh it's monday, if I eat this chocolate bar it will have gone by Friday when I WI so it doesn't matter"). I definitely agree that it can be a real mood spoiler though and on balance I think once a week is better.