This is a somewhat controversial question. Some professionals believe that daily weigh-ins are 'obsessive' and can lead dieters to become obsessive about their weight. They are of the opinion that weekly weigh-ins are ample and that you should not worry about the scale, but rather how you feel. I agree that the scales aren't everything, I always remind my clients that the scale isn't the be all and end all, it is just another feedback tool, besides how your clothes fit and how you feel.
However, I have always been a great advocate of daily weighing. Why??? Because it gives you instant feedback on foods that may make you retain water or cause constipation, etc. It also reflects your activity. Done a particularly tough workout and found your muscles feel heavy and swollen? You will also find you weight more on those days too! If you weight yourself every Monday and Monday just happens to be the day after you ate Chinese Food or the day before your "time of the month" then the reading is not really a true reflection of your weight.
I usually suggest my clients record their daily weight on a graph. You will soon see if the line is going downward (if weight loss is your aim) or is staying stable (if weight maintenance is what you are trying to achieve), even if there are some ups and downs along the way!
A recent study supports this as well. Dieters who weighed themselves daily were more likely to not only lose the weight...but, most importantly, KEEP IT OFF!!! The results were even better when combined with social support - online training forums, group training, personal training and friend and family support.
So, drag out the graph paper and get started!!! (Nude weight first thing in the morning is probably the most accurate).