CVS has nice ability to substitute keywords with values, and I really miss this ability in some other proprietary revision control systems (... cough ... ClearCase ...). Examples of CVS keywords are:
Keyword substitution usually happens by default for all text files. But this default can be changed using cvs admin command with one of the -k flags, whcih changes keyword substitution mode. Examples are:
So, when keyword substitution does not work for some reason - check the substitution mode.