The heaviest lens I used with my GH2 was an Olympus 14-35mm f2, which weights 1.98 lb (900 g). I used it on a three day shoot, the camera was fine but I think I was pushing it....
On the Lens side there is none, (don't know if this is constant, or a fluke) on the GH2 side its about .5mm (which is enough to be annoying)
For me- I don't like touching the GH2 when I am filming, (touch the lens only: Focus/FaderND/Aperture) so this is a non-issue. The adaptor is so steady for the lens that it is worth it.
Hopefully I can 'rig' something to make the M43 as ridged as the Nikon mount. Any ideas?
The max I`ve used for long periods of time without a tripod colla r is about 3 pounds. I`d probably second the reccomendation for a collar when going over 2 pounds (unless you are shooting handheld and supporting weight with your other hand, or using rails).
Some of the vintage teles don't have thread holes. If you have rails you need an lens support. Or you can try your camera store for a collar -- hard to match them on line. Best to buy it in a shop so you can make sure it fits.