Sorry to bump this up but after reading the entire thread, it seems that everyone is focused on two lenses. Those lenses ahve dropped in value on the used market because of over saturation in the market and because of obsolescense with regard to a better product. I bought the Siggy 35 and tested it same day against a CPS 35L loaner. The Sigma was sharper. So why pay $1100 or whatever for a product when I can get something better for a couple hundred less, brand new?
The second thing I noticed was that some people don't care about the depreciation their lenses may take. It seems to me that these people have also claimed their lenses have made them money. It really makes no sense to compare a hobbyist with a business when it comes to rationalization of buying a lens because the business can write the purchase off or depreciate it and build it into their pricing structure. A hobbyist may be more concerned with residual value since they are not making money from their passion, nor are they able to get any tax credit from the purchase.
So I guess what I am trying to say is that people argued apples and oranges.
Overall, I have seen that the Canon versions do hold their value well over third party lenses. Partly because they are great lenses, and partly because the third parties seem to update their stuff a lot more often or change design in order to compete with the more expensive name brand and to gain market share. More updates mean more old product going for a discount as people buy the latest and greatest. If Canon released a new version every three years the old stuff would lose value faster.
I'm thinking of picking up a V2 of the 70-200 but have concerns as the third party people have versions that are relatively close in performance with the L version. So if I buy the L, I am taking a gamble that the resale value will hold, as I don't plan on making money with it. (plus the timing of a purchase can be exerything, considering refurb lenses and rebates)