1) Flag Register
A flag register is most often used by me as a "quality" or "confidence" accumulator.

All flags reset could indicate "currently normal" ( A real time status or confidence value).

Or all flags reset could mean "no exceptions occurred" as the result of a complex sequence of events where each event maintains it's own error or exception flag (Status Result).

2)DUMB FLAG NAMES
I still agree with you Andy. It's the 8051 (bits that are electrically and programatically derived) that causes us to ask interesting questions. I can think an application case where it would be ok (in my mind) to ask "What kind of Access Point Monitor is requesting service?" (sorry for the asm)

CLR ACCESS_ID_REQUEST ;Request type
JB DOOR,Door_Service ; IF door, branch

3)Exploiting FLAG REG's in C
As to a compiler's ability to allow you to exploit this technique i can't say much but read your manual. I would miss not having this capability.

regards,
p