Sacramento International Airport is not currently accepting reservations on AirportParkingReservations.com.
We have used the shuttle at least three times. We have never had to wait long for the shuttle and they are there when we come out. I think it is a good deal. Better than waiting for someone to pick you up or staying a hotel, etc.
I park in this lot every time I fly out of SMF. They have buses going around to pick you up constantly. Just be sure you write down what section you parked in. The lot is huge.