Being a skeptic (of AGW) I'd be skeptical about the claim too. What I'm not skeptical about is people dumping a perfectly good four cylinder car just to get into a hybrid. You are then doubling the carbon footprint on the manufacturing aspect to save a relatively small amount of carbon output, depending largely on your driving needs.
Well in fairness if you trade it in then it goes to someone else. So long as the car doesn't go to the scrap heap those effects aren't really a factor. Or so I'd think.
I was really just trying to give Rob a hard time, because it's fun. I would caution against rushing into a hybrid as most reports I hear is that they spend more time in the garage than comparable gas only models. And that's while still on warranty.
I don't know a lot of people personally who have them, but I've got one neighbor with a Prius and they love the thing. They've probably had it a little over a year. I haven't read up on them because I haven't been in the market but I'd think that if there were serious problems with them, we'd all know about it and sales would be poor.
As for saving gas, the only real way to do it is to drive less. Which is what I try to do. I hate driving. I've even cut a way back on SW runs. Barely do that at all nowadays.