You may have seen this site: http://www.photozone.de/8Reviews/index.html that reviews lenses, including several Zuiko digital lenses. I don't know how valid it is, though I'm pleased to see strong results for the Zuikos (consistent with magazine reviews). The biggest complaint it has is with the 50-200mm f/2.8-3.5, which is a favorable review overall but which finds quite a bit of vignetting wide open at full tele. Before I bought mine I tested it at the store and I've done so since. I can't say my test is at all scientific; I can only say that I can't see any sign of vignetting with the naked eye. This is with shots at 200mm and f/3.5 (wide open at that end). I pull the shots into CS2's lens correction filter and I can't see a thing to correct. Possibly I'm just blind in an eye, but the review found almost a full EV corner darkness. I do think I can see that! Possibly Olympus has corrected it either in production or in the software updates (which I always utilize).
By the way, I have a post under "Catch-All" on lens weight, as I'm concerned about how heavy the Zuiko 35-100mm f/2.0 is (not to mention pricey). Anyway, if any Oly users have experience with it I'm sure that we'd be interested in your findings.