Are there a lot of poor copies of this lens? The only reason I ask is that a lot of the examples which are sold on here are literally weeks old, and some have sold more than once. I've been looking for a replacement for my 17-85 and now that I have a Sigma 10-20mm and a Canon 70-300 IS, I would quite happily go for the likes of the 17-50, however it seems as if its pot luck to get a good sharp copy with no focussing issues.
