I do it on Fridays. I used to do it every day. More than once... I was a little obsessed. But Friday is great because it's before the weekend so motivation through Saturday and Sunday will work out if I did well and it's at the end of the week so I can get a more accurate count of how I'm doing.

I was weighing in on thursdays. Now I think I'll weigh in on sundays since that's when the year starts. =)