Eyebrows are a fine thing indeed, and though I'm not a big fan of plucking them, I do have one thing to say: eyebrows (IMO) look much better when they have some shape, and are not simply lines. Also, shaving them into triangles gives the appearance of being constantly angry, ie Pamela Anderson.
All of this obsession with eyebrows - especially among women, although as another noder mentioned it is becoming popular among men - leads to one obvious conclusion, and that is that eyebrows are a factor in physical attraction. I can only wonder why this is. There is, however, reason to believe that the "original" purpose of eyebrows was to express emotion. Knowing another's emotional state is important in judging how to react to them. In a study by Paul Ekman of various cultures, most people from every culture he quizzed could recognize the facial expressions from other cultures. Countries tested: Brazil, Chile, Estonia, Germany, Greece, Hong Kong, Italy, Japan, New Guinea, Scotland, Sumatra, Turkey, and the United States. The emotions tested were anger, happiness, fear, surprise, disgust, sadness, and contempt. This suggest that the facial expression and recognition of emotions is universal, and has developed through evolution, not through culture.
One last thought: no matter how late it is, and no matter how badly you want to play with the electric hair trimmer, DO NOT shave your eyebrows off. You will look like a cancer patient/martian. I know from personal experience.
. Carole Wade and Carol Tavris. Sixth edition, 2000.