Just to clarify, this thread is for photos taken in the rain? Not photos of wet kit?
These two were taken on a rather wet summer's day. Heavy showers kept coming, and I kept shooting with the 7D+100-400L unprotected. This was fine until I noticed the contrast in the viewfinder dropping. No problem I though, just a bit of condensation on the viewfinder. Wiped it and... didn't help. Oh dear. Looking closer, the 100-400L had a load of condensation in it. The tiger was one of the last photos I took of it before I gave up. Switching to another lens fixed the visibility, but the AF felt a bit off. Possibly there's condensation in camera too...
It happened again on another trip, when I decided to get the 70-300L as my wet weather kit. Also considered the 70-200 II but it didn't seem worth it for this application. So far the 70-300L has held off the rain. The 100-400L's weakness I think is its extending part of the body, when exposed and zoomed a lot it lets moisture in. Sealed lens mounts seem unnecessary to me as water ingress there has never been a problem. Just need the lens body to be sealed primarily.
Can't remember if I was using the 100-400 or 70-300L for this one. Was only lightest rain at the time and no bother to the kit.
Side note: On the 7D, I've also had the rear joystick play up if used in the rain a lot. Clears up after drying out.