Just FYI, I started a thread over at APUG on my long-term impressions of the 90/2.0 Macro, with plenty of examples (and others have also contributed), you may want to have a look:
http://www.apug.org/forums/forum52/65556-om-zuiko-90mm-f-2-0-macro-long-term-impressions.html
The 90/2.0 is no mere lens, it's one of those rare examples (like most Leica M lenses) that seems to define the lens maker's art. It is simply exquisite, which is why a second-hand example of this 1980s lens costs more than a new modern ~100mm Macro with electronic image stabilisation and focus that goes to 1:1 (the 90/2.0 only magnifies to 1:2). And having both in hand, I must say that the Zuiko 90/2.0 is built far better (feels more expensive, more solid, more jewel-like) than a $3000 Schneider Super-Angulon XL 90mm f/5.6, the only other lens I own which I would classify as "exquisite" or [insert similar over-the-top hyperbole here].