Wow...I never knew that bowing had so many different meanings...
“Bowing has many functions in one. It expresses the feeling of respect, thanking, apologizing, greeting, and so on. It’s a convenient and important custom for you to learn. You can bow, when you say, “Thank you”, “Sorry”, “Hello”, “Good bye”, “Congratulations”, “Excuse me”, “Good night”, “Good Morning”, and more.”
“...there are different ways of bowing. It depends on the social status or age of the person you bow to. If the person is higher status or older than you are, you should bow deeper and longer. It is polite to bow, bending from your waist.”
http://gojapan.about.com/cs/etiquetteinjapan/a/bowing.htm
Then there is the bow when you fall in love. Thats a very esoteric one.You might call it the unrequited bow, full of capped passion. Ever see a volcano bow? You get the idea.