Daily for me, before shower. Twice if you count a wii fit session if the weather is bad and we can't ride.
The big thing with weighing daily is that even if you weigh in at the same time and same point in your morning routine, you will see the number bounce around day to day, and not always in the direction you want. I've been doing this for several years, so it doesn't phase me if it jumps a pound or two for no good reason, and likewise don't get overinflated if it drops (it will come back up the following day, guanteed).