In fact, travelers are flying more and driving less, with the largest decreases in spending seen at car rental services for consumer and business groups.

FORBES: Luxury Travel Spending Up Despite Gloomy Economy

There are at least three things that make the rental-car business great for customers but utterly detestable for investors.

FORBES: Connect

Frequent business travelers are the most lucrative customers for car rental companies, and when they travel someone else pays their bills.

FORBES: Why Car Rental Companies Can Charge $9 Per Gallon for Gas