While we're over here debating the merits of harem pants versus skinny jeans, Sudanese journalist Lubna Hussein has been fined $200 for wearing pants (but was spared 40 lashes). Sudan is partially ruled by Islamic law, and the statute in question is conveniently vague, singling out anyone “who commits an indecent act which violates public morality or wears indecent clothing” for punishment.
Plenty of religions and conservative groups argue that God really prefers women in skirts. Even in the secular world, in more conservative (i.e., traditionally male-dominated) professions female employees are encouraged or even required to wear skirt suits. Yet pants are arguably more "modest" than skirts, given that they generally obscure the shape of the leg and cover more of that tempting flesh.
Clothing for women has often served as a battleground for women asserting their social and political rights: consider the 1920s, when flappers chopped off their hair and traded Edwardian hobble skirts for short shift dresses while suffragettes clamored for the right to vote. Yet pants didn't really become completely acceptable for women in polite society to wear in public until the 1960s, despite such early adopters as Marlene Dietrich and Katharine Hepburn.
Ironically, in our society, it's now men who have to deal with the most societal strictures against diversity in their wardrobe—perhaps one reason that skirts for men haven't quite caught on. (That, and their hairy legs.)
UPDATE: Hussein was released from jail Tuesday, where she was sent on Monday for refusing the pay the fine (it was apparently paid by a journalists' union). She says she'll continue to wear trousers.