Short answer (from Dvdtalk):
For Warner Bros titles: Initially Warner Bros had announced that they were going to be RCEing their titles but aside from South Park none of their titles are infact RCE. Here's an official update from Warner Bros:
Please note the following titles DO NOT HAVE RCE:
Best In Show
The Perfect Storm
Proof of Life
Superman, The Movie
Currently Warner Home Video does not implement the RCE. The only title I can confirm is South Park, which only distribute.
VP - Publicity, WHV
If there's new information as to whether Warner has indeed started RCEing (hehe) their dvds, please post. Current information states though that Warner does not implement RCE.