http://www.autoexpress.co.uk/news/autoexpressnews/220173/andrew_englishs_column.html

Although it's mostly typical short sighted "most electricity is not carbon emissions free" BS I found a couple comments interesting. In particular these two lines.

GM planning a launch of the Volt, which uses the chassis frames from the forthcoming replacement Vauxhall Astra, in 2010.
3/08 "spy photo" of new Astra.
http://www.caradvice.com.au/wp-content/uploads/2008/03/opel-astra-003.jpg
and
Volt is a very sophisticated vehicle, but on the surface it is a conventional (if very aerodynamic) five-door hatchback

Obviously either this guy has things confused or has some very different information than we've all come to believe. I'll add only that I participate in a GM sponsored survey site that had one survey asking opinions about a Volt spec car that had a hatchback design very similar to the Astra...so it doesn't seem totally out of the question...perhaps the second generation?

Based on snippets from various media sources, I suspect that the vehicle will have the functional aspects of a Buick Rendevous:

http://images.automotive.com/cob/factory_automotive/images/features/auto_shows/2006_CIAS/2006_Buick_Rendevous__Rear.jpg

To me, the Volt is starting to look more like a crossover vehicle.