I purchased a Honda NGV (compressed natural gas) Super Low Emissions Vehicle http://automobiles.honda.com/civic-gx/ in June 2007 in order to lower my carbon footprint. As a Realtor I usually average 1200 to 1500 miles of driving per month. I now have PHIL, home refueling unit, installed in my garage.
I've discovered this car is very economical to operate. The convenience of being able to refuel at home combined with the cost savings makes this car well worth the investment.
Using PHIL http://www.myphill.com/, which fills the tank at a higher compression than the local Natural Gas Utility filling station, the car goes for 230+ miles (instead of 140 miles) before the refueling light goes on. This has eliminated a great deal of the anxiety that I used to have about running out of gas.
On longer trips where refueling remotely is needed, its important to plan and know the location of more than one accessible refueling station ... just in case. I have found that refueling equipment at stations in other parts of the state are not standardized and operating them is not always straightforward. Also some refueling stations don't take standard credit cards, or even cash.
I was skeptical that the cost savings would pan out, but my actual fuel costs are running more than 50% less than the cost of my previous vehicle.
The biggest drawbacks to this vehicle are the trunk size and traction on dirt/gravel roads, but, like using alternative energy, I've learned to live with it. This is truly a clean, convenient, and cost effective car for short to moderate length trips.