When you guys say circuit breakers are you talking about the ones on panels in lieu of fuses?
If that's the case most that I have dealt with have been either left (off) right (on) or have been on toward the outside and off toward the inside (dual vertical rows with the shared inside being 'off').
Either way, I don't really think it matters one bit so long as you pick a format and stick with it throughout.
There is the other option of those little metallic surrounds you can buy for most toggle switches that actually say "on" and "off". Not much room for confusion there.
Of course you could look at it as boat security: don't want someone to be able to easily steal your boat -- make every single switch go off in a different direction that only you know!
