I guess this is a better place for a more formal critique. Here is my take on this as a designer:
I feel this iteration is a step backwards for a number of reasons. The design as a whole is much less familiar as an iPhone and an Apple product. The classic silver bezel is gone as are the simplistic lines that grace all of Apple's industrial designs. By removing the curved backing, Apple has taken away ergonomic considerations, something they were careful to champion when the first iPhone and even the iPad were released.
Taking this a step further, the transition between the glass front and the aluminum center housing is awkward. Evidence by the close up images provided by Gizmodo, the materials are not flush and come together more like tectonic plates than a finely tuned industrial design. There are also smaller design inconsistencies, including the volume buttons, which no longer have their contexts defined. What this means is that the previous volume rocker made it clear that the top was volume up and the bottom volume down. These new buttons, perhaps to Apple's benefit, are no longer as strictly defined.
Overall, the 3G/3GS seem much more well executed and resolved. I will be disappointed if this turns out to be the real deal, but I am extremely doubtful.
I agree, but Apple has seemed to go for more sharp-edged designs in some products: the iMacs for example have become less and less rounded throughout the years, the windows in OS X and so on, have also adopted more well-defined angles. The Magic Mouse is also totally sharp compared to the Mighty Mouse (okay, we should call it Apple Mouse...). Also, you can see Edge-to-edge glass on this "new iPhone", something introduced on the newest iMacs.
I think the fact that the back and the front of the device are both made of flat, dark glass-like material is more a sign of consistency and symmetry.
I agree that the round, separate volume buttons are strange, up and down volume should be linked, but as you say, there might be a reason for their separation. Maybe this device is just a prototype, and some minor things may still change until the final one is released.
The aluminium center and the black screen and back reminds me of the MacBook Pro designs (and iMac, iPad for that matter). Matt silver and shiny black, it's something Apple seems to like at the moment.
The seams are strange indeed, but maybe they are really to allow a replaceable battery, in which case they are not unnecessary, but take away from the device's harmony.
All in all, I feel that this design is more "modern" and less "organic" compared to previous iPhones and previous Apple products, and this does seem to be the direction in which Apple is going at the moment.
I feel that theoretically, this device matches up with what Apple would do next with the iPhone, but may be a bit unpolished, mostly because of the seams and the round buttons. However, since there is still quite a lot of time until the new iPhone is released, I think it's totally possible that the design may change either totally or just a bit.