GM seems to be pushing more on the truck-hybrid front. My understanding is that so-called "light hybrids" (much like the VUE GreenLine) are their choice for this market. The tech is not particularly demanding -- uses a motor-generator in place of the alternator, and regenerative braking -- is fairly easily retro-fitted to existing platforms (witness the VUE and a Chev truck to be hit market very soon) and gives a small but significant boost in mileage. If you look at the economics of the Prius, even its impressive mileage claims are blunted by the price increment over say a Camry (similar carrying capacity) -- payback wouldn't be until the 100,000 mile range.
Disappointing sort of "half-step" that it is, GM may actually hit a profitable segment their way -- trucks (and by extension SUVs) have been one of the profit-mainstays of the North American manufacturers for years, and anything that will increase market-share is looked on favourably by them, especially if it isn't horribly expensive. It is widely rumoured that as notable as the Toyota Prius may be for bringing very complex control tech to market, the reason for rolling out that tech to other models (400h, Camry) is to broaden the market in hopes of some kind of "economy of scale" that might make at least a LITTLE profit possible.
Sorry, but to me, putting 2 drivetrains into a car in hopes of getting the best from each seems to be a REALLY expensive approach to the problem -- the long term costs (battery replacement, etc) are likely to be prohibitive.