I recently began this practice myself. I have a co-worker who lives on my route to work. I suggested to her that we might share a ride, thereby cutting our gas bills in half and saving the planet at the same time. She was all game!
So, it's been working out great. With gas costing in excess of $4/gallon, sharing that cost with someone else has been completely worth it. The added benefit is that we've taken one more car off the road during the busiest times of the day.
What are you waiting for? Put out an e-mail to your colleagues and see if someone lives near you, or if you know of someone who does . . . ask them to share a ride! There really aren't any downsides.
Click here to see how your car compares on fuel economy!