If the car battery is anything like the batteries in my xbox controllers, then I'm not putting much faith in the cycles per lifetime of the car battery, meaning it won't be long before i have to invest 10k or so into another battery.
The XB360 controller uses Ni-MH batteries and a really cheap, crappy charger. This is about the worst possible scenario. They'll die quickly.
The Volt and Leaf are using Li-Ion batteries. I don't know how good the charger is. If it's done right, you can cycle it all you want, and it won't matter. The only thing that will kill them is time and heat. Articles I've read indicate that GM is limiting the charge/discharge thresholds to 90%/25% in the Volt which should easily double or triple the lifespan of the battery compared to the 100%/5% thresholds you see in consumer electronics. The cells are also probably engineered for longevity over energy density, if they're thinking about it right. I don't know how good the charger is, but the articles I've read make it sound fairly intelligent (it probably does columb counting and has full V/I control). Given the conservative thresholds they've picked, I suspect they put some thought into it.
My biggest concern would be heat in a vehicle application. We all know how hot a car can get on a sunny day, even without engine heat. Lithium Ion batteries degrade up to twice as fast at just 100F as they do at 70F. I'm not sure how or if this has been addressed in the Volt. It's possible to make some tradeoffs in the design of the battery cells themselves to combat this, and this may have been done in the Volt, the Leaf, or both.
GM is guaranteeing the battery for 8 years or 100,000 miles. That's a heck of a warranty, so I'd say they at least think they've got things sorted out. Now, whether neo-GM can survive another 8 years without going bankrupt (again) is anyone's guess.
That said, yeah, they're still too damned expensive. No way I'm buying a first-gen car based on a new technology from GM (with all their recent history) for $45k+. I'll give them a few years to work the bugs out and probably bring down prices, too.