I bought Rob and I FitBit Zips in March, WAY better than any pedometer I've ever had. The Zips are simpliest which suits us, we don't give a hoot what everyone we know is doing via facebook
Because they do have a little chip they use up a battery a little sooner, with a brand new battery it lasts about six months, the factory one might not last that long.
Rob wears his on his shirt pocket or jeans pocket, I clip mine to the center of my bra.
When you get it you go online to FitBit to register it and get it going.
Weight and height input when you register gives your FitBit the correct stride for you.
I doubt I'd have used it if it had been a wrist one, just me.
I heard about it from one of the participants on the monthly weight loss thread.
Some insurance companies will pay for it.