My daughter and her boyfriend flew them this morning to Myrtle Beach. I was impressed. Free parking I agree is a bonus, and you can't beat their prices (and they run 24 off or 35 off, tons of specials). There is no line for security, so you don't have to necessarily waste 2 hours there, one hour would be fine.
One word of advice would be to pay for your seats. On the flight this morning, it was completely full, but they had six inoperable seats. They would looking for volunteers, but if they did not get any, 6 people were getting bumped (they were getting a free flight in return I think). I asked if my daughter could get bumped, and was told no since we booked well in advance. But the gate agent said the way to always make sure you get a seat and not get bumped would be to pay for one in advance (I had also paid the cheapest category, $10, when I booked so they were safe).
I don't mind paying for luggage and carry ons, it seemed to cut down on the usual flight full of roll-aways. One thing I thought was confusing was adding luggage. The website says at booking or 24 hours. I took that to mean 24 hours before the flight, but it means 24 hours after booking. I added it when they checked in on-line, for $33 (they shared a suitcase, and only needed it one way, someone else drove it down for them since they were meeting with other family members). It was a difference of $5, and my misunderstanding, I thought it was going to be $28. So my advice there is buy your luggage when you book the ticket.
Also, make sure if you try them to check in on-line and print out your boarding passes at home. Starting next week they will be charging $5 for each one if you print it out at the airport. Despite all the nickle and diming Spirit does, it was still hundreds cheaper than other flights we looked at. Southwest and Jet Blue are still my favs, but all in all, their experience this morning was a good one. I much prefer the quaint feel of Latrobe to PIT. Plus the restaurant and bar looked good (unfortunately not open in the morning though).