Bad weather can delay flights by hours or days. This can cost you valuable vacation or business time, and can even leave you stranded at the airport. If your flight is canceled, you'll be competing with hundreds of other passengers for hotel rooms or alternate flights, which can be very expensive.
Traveling by air is often more expensive than traveling by train, bus or car. A direct flight from Cincinnati to Milwaukee may take less than an hour, but it can cost hundreds of dollars. It's often cheaper, though more time consuming, to buy a few tanks of gas and drive to your destination.
Most airlines, especially budget carriers, charge baggage fees for any luggage you check in. As of September 2010, one airline (Spirit) even charges for carry-on bags. This can add hidden costs to your trip, especially when you must take a lot of luggage along for a long vacation.
