First of all, air travel, especially in the US, is extremely safe. Personally, I have flown nearly 500,000 air miles and have had no major issues. There is always a chance of turbulence -- higher in the summer than other times of year -- but planes are built to withstand enormous amounts of shaking without any structural damage.
Spirit was formed in 1980, so it has been around for a long time. It started as a charter only operation, and expanded to scheduled commercial service in 1993. Spirit is a "classic" low cost airline, and will charge you for any checked bags, and will also charge you for drinks on the flight. However, their fares can be quite low to begin with.
Spirit Airlines flies only Airbus aircraft, such as the A-320. If it makes you feel any better, all of the recent airline 'woes' have involved Boeing planes, like the 737 and the MD-80.
Spirit's planes are the newest in the Americas
. The average plane age is 2.1 years, which means you are flying on modern, up-to-date equipment.
Spirit has had two non-fatal incidents -- which is very low, considering that commerical buses have many more, proportional to the number of riders. Think about all of the auto accidents you hear about on the radio each day! Imagine if there were only auto two accidents since 1980... that would be pretty good!http://www.ntsb.gov/ntsb/brief.asp?ev_id=20051025X01717&key=1http://www.ntsb.gov/ntsb/brief.asp?ev_id=20020612X00866&key=1
Spirit Airlines has had no fatal accidents in its history.
Let me know if you'd like to talk about air travel any more :) I'd be happy to ease your mind futher.