Well you guys know they are implementing new EPA figures closer to real world driving for 2008 right? So those V8 figures will be worse than expected. But the V6 won't be retaining the 21mpg highway rating either.
Keep in mind the Titan gets 18mpg highway with this engine (under current EPA ratings) with an extra half ton of weight and more surface area... Unfortunately the new V8 path is supposed to be some AWD only so that will nick some of the increased eco over the full sized rigs.
If your buying a a truck based SUV and not some softroading poser youve probably already commited to the realization that your fuel eco is going to suck, allot. Especially if your one of those dumbasses that thinks a truck just doesn't look right without 31"tires.
The Armada isn't going anywhere, they just redid the interior for 08 to differentiate it from the Titan's as well as the roof racks and a number shared outside cosmetic changes they made on the Titan (still one of my favorite trucks). Look at Toyota they have 3 V8 SUVs (4 Runner, Land Cruiser, and Seqouia) so is more of Nissan conforming to the competition than doing anything radical.
On a side note when it comes to looks (and looks alone) the new Tahoe is probably the best looking fullsize SUV out there. That said I'd probably set fire to my genetailia before buying any GM product.