One example is the Lumix G 12-32mm f/3.5-5.6 (my review) pancake zoom lens, seen below (to the left) compared with the older Lumix X PZ 14-42mm f/3.5-5.6 (my review):
The older black lens has a plastic body, while the newer silver lens has a bare metal surface.
But is the new lens better, with the external aluminium body? In terms of handling, I certainly like the old lens the best. It has a ribbed ring around the base, which is good for gripping when mounting the lens. The new lens has nothing of the kind, and is quite slippery to handle.
There is, however, a textured ring around the front, which is used for extending the lens and zooming. The older, black lens does not have a zoom ring, as the motorized zoom is operated with a lever.
I guess the purpose of the metal surface is to make people think that this is a high quality metal lens. However, is it really a metal lens?
Some people have reported that the front metal surface has come off, revealing a plastic construction below. For me, the rear ring came off, and you can see clearly below that it is just a very thin layer of aluminium, which is glued to the plastic chassis of the lens:
Personally, I don't mind the plastic construction at all, in fact, I think an all plastic design would have been superior: It could have been textured for a better grip, and the surface would not come off accidentally, as it could have been part of the chassis.
Now, I am sure that if I had taken the lens back to the retailer, they would have sent it for repair at no extra cost to me. But this is a hassle, and I would much have preferred a design which does not put a thin, fragile metal surface on the outside of the lens.
By the way, here we see that the metal ring is prevented from rotating by a small "tap":
Not only Panasonic is doing this, of course. Some people have been angered by the fact that the pro grade Olympus 12-40mm f/2.8 has a plastic construction beneath the metal surface.
And the new Samsung Mini-NX system has metal clad camera bodies and lenses:
Just to mention a few. I think to put a thin metal surface on all consumer electronic devices is a strong, and, sadly, dysfunctional, trend.