Integrate with Jawbone UP
This one seems to be taking off. They just bought BodyMedia.
I think Omron is the most popular pedometer of all but I don't think those pedometers upload their data.
Voila! http://beeminder.com/jawbone (more official announcement coming soon)
Christopher Merrill commented
Jawbone recently added the concept of "partner apps" that connect to their service -- that seems like one way to get that integration going.