I don't think there should be any rules whatsoever for away messages. They should reflect the mood of the person, or be an outlet for whimsy, funkiness, anger, or whatever floats one's boat. Of course, this is from a person who never sets a relevant away message, and quite often sets some that are utterly incomprehensible to her friends (i.e. " but I'm not pretending to be a potato.") So I'm not really sure how sound my opinion is.