The most immediate problem that can result from wearing high heels are callouses, corns etc. Also, the muscles and tendons in the back of the leg accommodate and will over time become shorter unless you regularly change the height of shoes you wear. That's why if you want to work out your calf muscles you should wear heels one day and flats the next.
Bunions can be caused by high heels - particularly if they are tight (like stilletto heeled winkle-pickers. Also, you can exacerbate back problems due to having to redress the shift in balance.
If you wear a 3 inch heel, all your body's weight is concentrated on the ball of your foot. This causes your calf muscles tighten and your toes have to grip your shoes or they get squashed.
Scientists from the University of Helsinki in Finland found that supervisors believe tall women have more management potential than their petite colleagues, regardless of their ability or education. So wear high heels if you want promotion!