2 ounce copper is theoretically very good.
The runs in a typical CPU power layout (nothing else draws as much power from the PCB as the CPU) are very short, though, and I doubt it'll help at all, as in any contemporary mainboard the weak link are the active devices and inductors, rather than the PCB itself. In most current designs, the designer may choose to route power through multiple layers rather than a single layer, essentially achieving the same results but with lower overall stray capacitance (specially if the power and ground planes are alternated).
1oz copper plane on a board that size is good enough for 20 amps or so, which is much more than the CPU can ever hope to draw in any kind of condition except fault states. That's 250 watts.
Actually the 2oz copper is far more difficult to solder as it acts as a big heatsink, and needs to be reflowed at a higher temperature than a 1 oz board, and the preheating is also done for a longer period. All in all, I'd say it's a bit more of a gimmick than anything else, but I'd be willing to be corrected on that - since we don't have the same board with less copper, we won't be able to see a direct comparison.
The only possible benefit is cramming in more traces into a smaller space, as you theoretically halve the trace width when you double the copper content of the PCB. That could result in more power phases, for example, or a more compact layout, or reducing the number of layers in the board.
Still one bad-ass board, so hope to see some results soon. I hope the pricing becomes reasonable soon (it won't be, to start with).
