An interesting article appears in the Sun Sentinel today, regarding tire rolling resistance and the effects on fuel economy:
http://www.sun-sentinel.com/business...,7641450.story
It is by an author who works for the L.A. Times, so the same article probably appears in other papers also.

The take-away lessons are:
1. Tire rolling resistance matters;
2. Do not trust the tire salesman;
3. Starting 2 or 3 years from now, tires might be labeled for rolling resistance;
4. Until then, it's hard to find information about rolling resistance.