Both the "Leica" (It's a panasonic, made in Japan) Nocticron 42.5/1.2, and the Olympus M.Zuiko 75mm f/1.8, are stellar lenses, probably the best in Micro Four Thirds. My friend and I did careful comparison, and the 75mm is the only Micro Four Thirds lens that seems to match the optical abilities of the Four Thirds SGH zooms. None of the others come close (this includes the M.Zuiko 45/1.8) - and most of the micro four thirds lenses require significant digital correction of distortion, and sometimes Chromatic aberration - thus severely limiting image performance.
Fahim - I'm not attacking your beloved M lenses - I'm just saying that they - nor most any other lens - are magical. I would certainlly be careful of Leica's marketing material. They are a company that markets luxury goods, not working equipment. They are constrained by the laws of physics.
With regards to the Olympus SHG f/2 zoom lenses - and please don't confuse these with the small, consumer Micro Four Thirds lenses, these are beasts with 77mm filters, and the best weather sealing known to man - I would rinse them under the tap after a serious outing to the beach.
I enjoyed my time with these "perfect" digital lenses, but I sold them. Why? First of all, the four thirds system is simply too constrained by the tiny sensors. I am used to film, and the smoothness and dynamic range it brings. Second, I am tired of carrying around such huge lenses, perfection be damned.
I've switched fully to my small manual-focus Nikkors, and the Voigtlander Heliar 50mm f/3.5 on my Leica M3. I sold the large Summilux ASPH. When I want to use a large camera, I use my Linhof or my Mamiya RB67. Otherwise, I am enjoying my 1960s Manual-Focus, pre-AI lenses.
Would this image that I made yesterday have been better with a $7000 Summicron-ASPH 50mm? I don't think so. The "look" would be totally different than my $70 Nikkor-H 50mm f/2, not to mention that Leica doesn't have a sensor that can do this (yet) - this was on the fabulous sensor in the Nikon Df.
My Olympus SHG zooms couldn't make this image either. They'd make a sharper image, but with a much deeper field, and never capture this dynamic range. And they'd be bloody huge, not a tiny, 52mm-ring lens that fits in my pocket.
Layers of the 20th century
I really don't like Ken Rockwell, but he's famously said for years: Sharp lenses mean nothing to good photographers. Use what you enjoy - especially what's small enough to keep with you. In that regard, Leica M, or micro four thirds - does so well. I had a nice stash of old Nikkors, so that's it for me at this stage - I could not afford a stash of new M lenses
Have fun.