I got myself some digital scales with an accuracy of 0.1lb and I've found that I can fluctuate 2-3lb either way in a couple of days without much of a reason. Weighing myself once a week just wouldn't work because I could hit a dip one week and a peak the next.
I just weigh myself every morning at the same time and write it down on the same scrap of paper. The general trend is in the right direction so I'm happy. Digital scales rock!