As a rule, I do the following:
 
1) For BITNET, the userid and node are all uppercased:
 
        e.g.  GKM$FAID@QUEENS
 
2) For internet, the DOMAIN portion (as registered) is upper case, node
   names are lower:
 
        e.g.   [log in to unmask]
          or   [log in to unmask]
 
3) For internet, userids may any mix of upper and lower:
 
        e.g.   [log in to unmask]
          or   [log in to unmask]
 
   ** I respect the case as it comes in the message (mail) for signup **
 
4) For percent hacks, a double rule applies:
 
         e.g.  [log in to unmask]
 
and so on, as required.
 
/Geert