I've looked into it. I took pictures of my car, started an account, etc. I was very disapointed with how little you can make by 'renting out' your car. Similar cars to my small Honda were able to be rented for $5/hr flat rate. That probably doesn't even cover wear/tear on the car.
It ended up not being worth it for me, not to mention I didn't get a single bite about renting my car, which is surprising since I live near Chicago.