I stroll a few bike forums and always check out the "Post your bike" threads, etc. There are always a handful of bikes in there with Lightweight wheels on them.
I have never seen them on a bike in any race I have been to. Mind you, I race mostly in SoCal so you would think there would be some around. Not that I am on a search for them but maybe I just didn't notice.
Have you ever raced against someone actually riding Lightweight wheels?