This is a little painful to write, because I know lots of ladies who wear white pumps and swear by 'em. That said, they don't always look horrible--sometimes the shoes are really cute and make a great focal point of the outfit. When wearing white shoes at all though, you have to remember that everyone's eyes will immediately be drawn to your feet. If you've got fabulous feet and hate everything else about yourself, go for it. Otherwise, I'd really suggest playing up another asset.The sad thing about white pumps is that because they are literally the only thing people will remember about your outfit, the potentially super dress you may be wearing is easily forgotten.
Another more obvious point is that it is incredibly difficult to keep white shoes clean. Dirty white shoes are even more distracting than their clean counterpart.
A great alternative is nude-colored heels. They elongate the leg without distracting from your overall look. If you want your shoes to have some kick (har har har, I'm so funny), try silver. Not bright, obnoxious silver, but a duller charcoal-esque version. The eye will be drawn to your feet, but the rest of your outfit will be noticed as well.