If the main is a back fed device that plugs onto the bus, there is usually a limitation to the total amps of breakers connected to any one stab.
If the main breaker is plugged into a space that would normally be occupied by a branch breaker, I see no problem marking it as #1 and identifying it on the panel schedule as a main breaker. IMO, it would need to be identified anyhow to comply with 110.22.
[This message has been edited by Tom (edited 08-30-2005).]
Few things are harder to put up with than the annoyance of a good example.