I wish we had done more research on Spirit Air on tripadvisor BEFORE we bought tickets from them to travel from Boston to Lima May 11-21, 2011.
So we found a great rate on two tickets in September and decided we'd take advantage and go on our dream trip to Machu Picchu. We'd been planning, organizing, and getting ready for our trip until two weeks ago we get an email from Spirit saying, very nonchalantly, that they'd changed our itinerary... by 5 DAYS! New dates are May 7-22. We call and tell them this is unacceptable since we have jobs, dogs, and have planned a 10 day, not a 15 day trip. They tell us there's nothing they can do. We ask for a manager. Get hung up on. Call back, ask for a manager, and finally speak with Maria. She continues to tell us there's nothing they can do. We say "certainly you have to have other flights closer to our original dates," and sure enough they do. We switch to May 10-22. I request something for free for our trouble (luggage and seat selection since all is a la carte). She refuses. I yell. Eventually she gives in. Ultimately we got nervous that they might cancel our flights home and we'd get stuck in Peru, which isn't an option since my sister gets married a week after we return. Surprisingly it was INCREDIBLY easy to get a full refund from them (which showed on our credit card today, exactly 8 days after asking for refund). We purchased more expensive tickets through United that are non stop from Newark instead of several lay overs with Spirit.
Ultimately it all seems to be working out in the end, but please please please be careful and do more research than we did before giving Spirit Air your $$.