Initial impressions of IQ and focusing
It's small(er than my other cameras, save for the X100), and the image quality can be pretty damn stunning. But be prepared for a lot of frustration along the way. Especially if you've grown up with AF.
Manual focusing isn't a PITA but it can lead to missed focus. Practice is everything. Practice anywhere, everywhere. Know the minimum focusing distance, learn to focus fast.
High ISO is not as bad as people make it out to be. ISO2500 converted to B&W still has that magic.
You have more chance hitting the lottery twice in a week than nailing focus at f1.1 on a moving subject at whatever speed.[/LIST]
Leica lenses are excellent but crazy expensive. A Nikon 70-200 VR II (USD2.4k, B&H) is cheap compared to a current-gen 50 Summicron (USD2.3k). The new 50 Summicron APO ASPH is USD7.2k.
With wide angle lenses (24mm and shorter) especially 3rd party ones), watch out for color casts, focus shifts and other weird **** you never get in the world of Nikon/Canon, Hasselblad, etc
With tele lenses (75mm and longer), focusing is a b***h when shooting wide open.
Which means, you'll probably end up with a 28, 35 and 50. Summicrons (f2) give you a better hit rate compared to Summilux (f1.4) lenses when shooting wide open (obviously). And Summicrons are heckuva lot cheaper than Summiluxes.
There's is no such thing as a 'bad' Leica lens, regardless of age, and assuming it's in decent condition. The difference over the decades shows up in the character of the lenses, i.e. the way the image is rendered - contrast, micro-contrast, flare (which isn't ALWAYS a bad thing)
Shooting wide open *IS* the point with Leica. Otherwise, any lens looks the same at f5.6 and up. Not convinced? Search flickr for "Leica 90mm Summicron", "Leica 75mm Summilux" to see what I mean.
Oh, and unless you've mastered (2) above, shooting the Summilux wide open is not easy. Try it in so-so light, and get ready to lose it. Gets worse if you're shooting 50m or longer lenses without a magnifier.[/LIST]
On buying used lenses
Buy LOCALLY. Granted, you can get lenses cheaper from overseas, but given how damn sensitive focusing is on the M9/M9P, you'll want to be able to test the copy of the lens before you pony up the cash. Either way, it's cheaper buying a used 'older' lens (which beats most other lenses out there anyway) than the latest APO/ASPH designs.
That said, go check out prices of the 'new' and pre-ASPH lenses - it's usually not a huge difference, and the newer aspherical lenses do hold their value a hair better