I have never been one to remove them unless it's plastic and broke, that was before I came to this site now it depends on the bike. I like the big chrome Schwinn plates and also the aluminum Suntour plates. I have a ton of NOS plastic plates and a few nice chrome plates that I got with all the NOS parts my friend gave me from his closed bike shop. Look to the right in the photo below that is one of two stacks of NOS plastic DD's from the late 70's early 80's that I had/have.

http://i299.photobucket.com/albums/m...parts014-1.jpg

We went riding today with a friend who has a fairly new CF bike. (I believe from looking at the graphics that the brand name must be "TREK TREK TREK TREK TREK TREK TREK" and the wheels are Bontrager Bontrager Bontrager Bontrager". I think it had a model name but I wasn't able to read it.) I noticed his rear wheel had a DD, a little, small one made of plastic.
http://users.rcn.com/jimmuller/pics/Taylor_Jim.jpg