The video shows some of the tests I did with the Panasonic Lumix G X Vario 12-35mm f/2.8 on my AF101.
Read my blog post for more information (german) and links to other sources:
The lens seems to be parfocal, but during fast zooms the picture gets blurry for a short moment. And even if it's f/2.8 throughout the whole zoom range, there's some strange exposure-flickering going on while zooming. Maybe this is fixable with a lens firmware update in the future?
Lens breathing seems to be minimal (tested at 12mm and at 35mm). The OIS works just fine for video. All the strange jitter we know from CMOS-sensors is completely gone when working handheld.
In my opinion this lens is ideal for documentary shooters.
Update (8/9/13): You might have noticed that the lens produces an annoying click sound while zooming which could be picked up by a microphone attached directly to the camera. The clicks are not very loud but they are there, especially at larger apertures. Only between f/9.0 and f/13.0 the lens is absolutely silent while zooming.