I am a big fan of Park N Go! IMO it is much more efficient than parking at the airport. The bus picks you up right at your car, you don't have to worry about lugging your luggage to a bus pickup spot, and then upon your arrival they drop you right back off at your car, no walking around in the dark required. I have never waited more than ten minutes for a bus.
I do always make a reservation to guarantee my spot and because the rate is even cheaper when booked online. I parked for four days for only about $17.
The only thing they definitely need to do is pave their lot. I parked in a pretty far corner over the Thanksgiving holiday and that lot was flat tire inducing. I have usually parked closer to the entrance where the pavement is much more maintained. But, since their service is parking they could def make good use out of a pavement job.