so, after some time tinkering with my zii EGG (that is the developer's edition), i can give you a power-efficiency comparison to an ipod touch 1G, for a typical GPU task (rasterizer/fragment-bound). take it with a grain a salt, as some of the measures in there were not particularly accurately taken. yet, they should give a general idea.
all times are from full battery, just-off-the-charger condition, to system auto-shutdown due to low power. also, battery for the two devices are as follow:
zii egg: 3.7V, LiPo, 1200 mAh
ipod touch 1G: 3.7V, LiPo, 900 mAh
note that the latter data are not manufacturer's figures (apple do not give any), but to the best of my google search for replacement parts, and as such might not be correct.
test run was a rudimentary object-space normal-mapping frame loop, which can be seen and obtained from
here. the sleep functions on both devices were suppressed (auto lock: off) and both screens' back-lighting was set to minimal (ipod: manual, slider to min; zii: off, effectively producing a minimal backlight, visually comparable to the ipod's minimal).
so, the resulting times are:
ipod touch: 6h
zii egg: 5h 40min
also, it takes noting that whereas the fps on the ipod was a stable 60hz, the fps on the zii was fluctuating between 30hz and 60hz, most of the time at 30hz (about 75% of the time), due to the beta-version nature of device's power-managing software.
in terms of work done per supplied energy, the zii is about (900mAh / 1200mAh ) * (5h 40' / 6h) = 0.71 times as efficient as the ipod touch at this particular task, framerate fluctuations notwithstanding. if we take the fluctuations into account (and take the truly rough estimate of fps time percentages - i.e. 25% @ 60, 75% at 30), then the resulting index becomes 0.44. but because of the rough nature of the measurements, i believe we could assume the more general index of 0.5.
i don't know about you, but i find that comparative index to such a power-efficient gpu as the MBX lite, particularly coming from a non-gpu, quite satisfactory.