Just got my 18-200 IS, and I can't believe the lens creep. If the lens is pointed down at about 45 degrees or more, anywhere from about 35mm on out, it just keeps on going! I never had this problem with the Sigma 18-200 OS. It is possible I just got a bad copy, but if not, it will be back to the Sigma. BTW, the lens lock on the Canon is on the bottom of the lens - not a bad location, but I don't want to have to use it every time I shoot down. What a disappintment!
I just returned the lens to Best Buy, where the photo guy tried to tell me the lens had nothing wrong with it. (I did find that if you squeezed the zoom ring, it held position better as long as you squeezed, which is what I think he must have done.) I was wrong to call it "creep". It was more of a slide!
I've read many complaints about this with the Nikon version. It seems like most all of them have this problem. Let's see if most of the Canons do the same thing. Go figure. In spite of the nuisance, the Nikon version is a wildly popular lens in their camp. A lot of the press photogs here in Puerto Rico use it.
It wasn't on the site. I just walked into the local BB store and asked for it after a friend told me his local store had it. It wasn't on dosplay, either - the guy had to go "to the back" to get it.
