I say we start tomorrow April 1st, and no, this not a joke!
I have an Omron Walking Style pedometer, it measures steps, miles, kcal, and it breaks out the number of steps that are aerobic (60 steps a min or faster), it also tells time. It cost about $20 on Amazon.com. I carry it in my pocket all the time, I find it motivating. The thing I love about it is that it stores the info for 7 days, so you don't have to write your steps down every day.
I say for the challenge we post our steps once a week, on Thursday starting April 8th, and I'll put together a post showing the pedometer users in order of the steps they took. So technically the "prize" is your name at the top of the list and a "kudos" from the rest of us. The goal for all of us is to average 10,000 steps a day, and to challenge each other to get a little higher daily average by the end of the month.