It couldn't be any simpler, and you've already done at least 75% of it somewhere before: 1. You join and post a profile; 2. You join a group; 3. When you're going somewhere, you post the details of your trip; 4. If you need a ride, you search for someone going your way. When you attract or find a match, bingo. You're are now a "GoLo." In the best new medium social networking tradition, it's a public forum, so you don't have to approve just anyone for a ride, and people who give and get rides are publicly ranked. If "Tom" in Cincinnati is known for showing up late and smoking with the windows up, the GoLoco community will know about it. You can even do your best Yellow Cab imitation and charge for the trip, with the money (minus a percentage for GoLoco) automatically placed in your account.
There are a fair number of systems in place to give GoLo the best chance of success, though getting in cars with strangers should be enticing enough. In the mean time, I'm going to 7-11 in about an hour. Who's in?