Details abound in whitepapers, et.
This, however, is a tip, not a treatise, so on to the chase. Where shared files on a domain controller are concerned, this could cause some serious problems. Users that have permissions to operate upon a file will be denied access once the file is encrypted. Because of the way that EFS works, if there is no recovery agent defined in the effective policy for that machine encryption will be denied. If you wait too long, however, and someone has encrypted files, keys have been created on that machine that will allow any files on that machine to be encrypted by any logged-on user.