I think DonSchap hit on it. While it's certainly true that the optics of a lens will have an impact on how sharp the image is, from many of the images posted here, I think that things like contrast, saturation, etc., are having more of an impact on what people are seeing. I don't mean that as a dig towards anyone, just that many of the images are posted straight from the camera, so the white and black points aren't usually set.
Here's an example. I picked a test image with camera shake and motion blur on purpose. It was taken on a 6x7 Koni-Omega Rapid that has a really nice lens on it.
If you look at the histogram, you'll see that there are no true black and white points in the image. The curve starts and ends too far inward. This gives a grey cast to the image and kills the contrast and saturation. The original wasn't like this since the b&w points were set correctly at the time of the scan, but I moved them here to simulate the issue.
Here the black and white points are set correctly, and there is a slight boost in contrast and saturation from additional adjustments.
There is no change in the actual sharpness, but my guess is that people would feel that the second image has more "clarity". I think having good glass is important, but moreso, learning to edit images. Getting more familiar with editing techniques will probably yield greater results than spending a bunch of money on glass. Plus things like camera shake will kill an image far worse than a cheap lens.
This was taken using the Canon 22mm-55mm lens that was meant as an APX kit lens. I think I bought it for $80 new.
I used just a touch of sharpening, but it was a film scan, so it's hard to tell if it's the lens, my focus, or the scanning that added the slight blur. Just resizing can do it. At any rate, I don't think you can judge a lens by images that are meant for the web. A slight sharpen filter at this size will cover a lot of sharpness issues.
