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.
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).
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 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....