Answer to Question 1: Women's fragrances sometimes employ more overtly floral notes, or stone fruit notes like peach. But most scents are unisex in that it's 2012, and if you like it, wear it. No one will care what gender the brand marketed it to.
Answer to Question 2: See answer to Question 1.
Answer to Question 3: Some would be better to keep on a season-to-season basis. Grey Flannel, for example, works best in fall and winter. I wouldn't advise wearing it in the summer. Cool Water, however, works year-round.
Answer to Question 4: Your body. Or your clothes. Or both.