I travelled from Detroit to Las Vegas with Spirit Airlines in October 2011. I booked early and also selected my seating in the process.
Spirit first changed my flight time and then later cancelled it and switched me to another flight necessitating a layover in Detroit before departure. This cost me financially as well as in mental aggravation. I was also a member of their $9 club. Incidentally my previous flight with them was also delayed in departure.
I have not and I will never fly with this unscrupulous airline again. I would also recommend that others follow my example.
Review about: Spirit Airlines Flight Booking.
Monetary Loss: $600.