For mine, participation entails a yearly health screening. The screening measures blood pressure, BMI, nicotine usage, and cholesterol (via a blood draw).

Depending on the findings, you fall into 1 of 3 tiers, which results in a penalty on every pay check if you don't fall into the numbers.

I know someone who works for Blizzard; if they wear a Fitbit and meet the goal set on it, they get a healthcare discount or a small cash kickback, I forget which.

Found a detailed presentation of the incentive plan here: http://www.myablife.com/files/HIP-Presentation.pdf