Back at the end of June last year, Matt and I gave his car off to his brother in Fargo. Matt hasn't commuted in 5+ years, and we already had to take pains to use his car regularly. With me joining him at his school, we figured we'd use both cars even less. His brother needed a new car, so this was a win-win all around.
Thus far, car sharing has gone well. In the past seven months, we have had one night where we miscommunicated and both needed the car. This was rectified fairly easily. Other than that, we either go places together or take turns with the car.
The savings are good. We save a bit in gas, but most of our savings come from me not commuting to work (side note: this is the most amazing thing, and I love not getting in my car every day). We save about $300 every six months in insurance costs. I'm not sure exactly, since we lost the multicar discount.
The best part, however, is something completely selfish of me. Since we have started sharing the car, I think I have filled up the gas perhaps three times. Maybe less. Again, some of this is a function of not using much gas. We can often go three or four weeks without filling up unless we're taking a road trip or more than one trip up to the Twin Cities. In addition, Matt doesn't mind taking the car out for more gas and to run random errands.
In sum, I'm happy we gave up the other car. Maybe the impending kid will complicate matters more, but continued communication works wonders at making sure we can get where we are going. I'm hoping we can enjoy the savings and environmental friendliness of being a one car family for the foreseeable future.