Still pondering on my next lens. Eyeing the 17-55 f/2.8 in most likelihood. There seem to be some in stock on the Canon refurbished site for a pretty decent discount (as opposed to buying new). Anyone here buy lenses from the Canon refurbished store? Are there any gotchas? Are these as good as new? Is there more chance of dust, or scratches, etc or are they guaranteed to be just as good as the new ones?