Well, don't undersell Columbus. If I'm not mistaken, it's the most populous state capital in the country. There is a big airport there, built to be a hub, but built just before things got bad in the industry, so it was simply never utilitized. It's centrally located, and less expensive to operate out of than Pittsburgh was. It could be a good place to build a small airline from.
I didn't intend to undersell Columbus, I'm from Columbus and we have enough problems with our "college town" image

. I appreciate the good comments on Columbus. I did indicate it was an exciting opportunity for Columbus and had huge local financial backing. To expand, the city offered around $57 Million in tax incentives and Skybus raised around $230 million in startup capital (the most in history raised for a startup airline). A lot of the startup funds were raised from local corporate businesses like Huntington Bank, Nationwide Insurance, Wolfe Enterprises, Batelle, as well as support from Fidelity Investments and Morgan Stanley.
Your right that Columbus airport is built to support a hub. America West based their east U.S. hub here until 2003. Since then, the city has tried to attract an airline to make a hub here. After lack of interest, I guess they decided to create their own.
As for the "largest city", that's more of a "fact", but "not the whole story" thing. Columbus is also technically the largest city in Ohio. The city of Columbus has about 700,000 residents, Cleveland has about 500,000 and Cincinnati has about 340,000. Obviously, including metro areas, Columbus isn't as large as Cleveland or Cincinnati. However, I believe including the metro areas, there are about 1.2 million people in the Columbus area. Additionally, Columbus airport competes with Dayton airport to attract a lot of Cincinnati travelers. Cincinnati is a major hub for Delta. Delta basically monopolizes that airport and a trip 1-1/2 hours up the road can save many Cincinnati travelers a few hundred dollars.
I do think it's great for Columbus and that it has a lot of support here, but I think it's a lot to ask for Columbus alone to make Skybus survive, so they will need to be somewhat user friendly for someone trying to fly from Seattle to Ft. Lauderdale or Boston to LA because long layovers and booking each "leg" separately may be too inconvenient to justify any savings.