That's the first time I've read a problem with the quality of the 17-55mm. Every single time, on dpreview.com and stevesdigicams.com forums, the lens is given the highest respect and admiration from the owners. I haven't even heard of one being mis-calibrated. Even L lens don't look that different, in good lighting, compared to the 18-55IS. You buy the 17-55 for the faster focusing, better build, and the 2.8 aperture while retaining IS.
After few weeks checking reviews, searching comments on the web, I finally bought a new Canon 17-55mm f2.8 IS lens from eBay for $1100 (to save few hundred Australian dollars). Maybe like most of you out there, I think, I trusted Canon qualities, especially with a highly ranked product. But not this time. Half photos taken with this lens have the quality par with my 18-55 f/3.5-5.6 kit lens (<$100) and other half are very blurry. When checking its IS, with wide open (f2.8), photos with IS on even worse than those with IS off. Not happy with the lens, send it to Canon for repair (Sydney, Australia), expecting to be returned in two weeks (standard repairing time). After two weeks, called Canon and found out that it was still on the shell and no one has touched it yet. Anyone had similar experience like this with Canon? Should it still be a trusted brand?