I just added my car to the database but it's not showing up at all. Nor was there a confirmaion message saying that my car had been added. I named it "Colorado Prius".
You'll need to add mileage data before your car will appear on the main page. Either add at least one tank of data or override your lifetime mileage from the Edit Car screen.
Click the "Edit Your Cars/Tanks" link in the database. You will be prompted to enter your GreenHybrid login information. Afterwards, the second table on the page will request information to create your car. Following this, "Add Tank" data.
You aren't doing anything wrong. Sorry about the error. I had added a new script to the website and it happened to conflict with the database connection in the mileage area. It should be fixed now.