Answer: More than I thought. Wait till your three-year-old gets carsick in that seat, and you spend the next day and a half trying to track down just where that smell could be coming from.
Good News: She had just handed my iPhone off to big sister before getting sick.
More good News: I think I found the source on the second scrubbing. Seat is now covered in Fabreeze and is drying in front of the fire..... again.
Even more good news: When you are taking steroids on Spring Break, you have an unbelievable amount of energy to get things done. Things that might otherwise be irritatingly inconvenient. Also, while on steroids, your sense of smell comes back.
Take away for next time: Don't let the three-year-old play on the phone while the vehicle is moving.